How do I calculate someone s age based on a DateTime type birthday

Question

Given a DateTime representing a person s birthday  how do I calculate their age in years

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I often count on my fingers  I need to look at a calendar to work out when things change  So that s what I d do in my code   int AgeNow DateTime birthday        return AgeAt DateTime Now  birthday      int AgeAt DateTime now  DateTime birthday        return AgeAt now  birthday  CultureInfo CurrentCulture Calendar      int AgeAt DateTime now  DateTime birthday  Calendar calendar           My age has increased on the morning of my        birthday even though I was born in the evening      now   now Date      birthday   birthday Date       var age   0      if  now  lt   birthday  return age     I am zero now if I am to be born tomorrow       while  calendar AddYears birthday  age   1   lt   now                age              return age      Running this through in LINQPad gives this   PASSED  someone born on 28 February 1964 is age 4 on 28 February 1968 PASSED  someone born on 29 February 1964 is age 3 on 28 February 1968 PASSED  someone born on 31 December 2016 is age 0 on 01 January 2017   Code in LINQPad is here

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This may work   public override bool IsValid DateTime value         dateOfBirth    value      var yearsOld    double   DateTime Now Subtract  dateOfBirth  TotalDays 365       if  yearsOld  gt  18          return true      return false

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To calculate the age with nearest age   var ts   DateTime Now - new DateTime 1988  3  19   var age   Math Round ts Days   365 0

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int Age   new DateTime  DateTime Now - BirthDate  Ticks  Year -1  Console WriteLine  quot Age  0  quot   Age

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Check this out   TimeSpan ts   DateTime Now Subtract Birthdate   age    byte  ts TotalDays   365 25

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The simple answer to this is to apply AddYears as shown below because this is the only native method to add years to the 29th of Feb  of leap years and obtain the correct result of the 28th of Feb  for common years    Some feel that 1th of Mar  is the birthday of leaplings but neither  Net nor any official rule supports this  nor does common logic explain why some born in February should have 75  of their birthdays in another month   Further  an Age method lends itself to be added as an extension to DateTime  By this you can obtain the age in the simplest possible way    List item   int age   birthDate Age     public static class DateTimeExtensions            lt summary gt          Calculates the age in years of the current System DateTime object today           lt  summary gt           lt param name  birthDate  gt The date of birth lt  param gt           lt returns gt Age in years today  0 is returned for a future date of birth  lt  returns gt      public static int Age this DateTime birthDate                return Age birthDate  DateTime Today                   lt summary gt          Calculates the age in years of the current System DateTime object on a later date           lt  summary gt           lt param name  birthDate  gt The date of birth lt  param gt           lt param name  laterDate  gt The date on which to calculate the age  lt  param gt           lt returns gt Age in years on a later day  0 is returned as minimum  lt  returns gt      public static int Age this DateTime birthDate  DateTime laterDate                int age          age   laterDate Year - birthDate Year           if  age  gt  0                        age -  Convert ToInt32 laterDate Date  lt  birthDate Date AddYears age                      else                       age   0                     return age            Now  run this test   class Program       static void Main string   args                RunTest               private static void RunTest                 DateTime birthDate   new DateTime 2000  2  28           DateTime laterDate   new DateTime 2011  2  27           string iso    yyyy-MM-dd            for  int i   0  i  lt  3  i                          for  int j   0  j  lt  3  j                                  Console WriteLine  Birth date      birthDate AddDays i  ToString iso       Later date      laterDate AddDays j  ToString iso       Age      birthDate AddDays i  Age laterDate AddDays j   ToString                                      Console ReadKey              The critical date example is this   Birth date  2000-02-29  Later date  2011-02-28  Age  11  Output         Birth date  2000-02-28  Later date  2011-02-27  Age  10     Birth date  2000-02-28  Later date  2011-02-28  Age  11     Birth date  2000-02-28  Later date  2011-03-01  Age  11     Birth date  2000-02-29  Later date  2011-02-27  Age  10     Birth date  2000-02-29  Later date  2011-02-28  Age  11     Birth date  2000-02-29  Later date  2011-03-01  Age  11     Birth date  2000-03-01  Later date  2011-02-27  Age  10     Birth date  2000-03-01  Later date  2011-02-28  Age  10     Birth date  2000-03-01  Later date  2011-03-01  Age  11     And for the later date 2012-02-28         Birth date  2000-02-28  Later date  2012-02-28  Age  12     Birth date  2000-02-28  Later date  2012-02-29  Age  12     Birth date  2000-02-28  Later date  2012-03-01  Age  12     Birth date  2000-02-29  Later date  2012-02-28  Age  11     Birth date  2000-02-29  Later date  2012-02-29  Age  12     Birth date  2000-02-29  Later date  2012-03-01  Age  12     Birth date  2000-03-01  Later date  2012-02-28  Age  11     Birth date  2000-03-01  Later date  2012-02-29  Age  11     Birth date  2000-03-01  Later date  2012-03-01  Age  12

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Here s a DateTime extender that adds the age calculation to the DateTime object   public static class AgeExtender       public static int GetAge this DateTime dt                int d   int Parse dt ToString  yyyyMMdd             int t   int Parse DateTime Today ToString  yyyyMMdd             return  t-d  10000

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This is the version we use here  It works  and it s fairly simple  It s the same idea as Jeff s but I think it s a little clearer because it separates out the logic for subtracting one  so it s a little easier to understand   public static int GetAge this DateTime dateOfBirth  DateTime dateAsAt        return dateAsAt Year - dateOfBirth Year -  dateOfBirth DayOfYear  lt  dateAsAt DayOfYear   0   1       You could expand the ternary operator to make it even clearer  if you think that sort of thing is unclear   Obviously this is done as an extension method on DateTime  but clearly you can grab that one line of code that does the work and put it anywhere  Here we have another overload of the Extension method that passes in DateTime Now  just for completeness

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A one-liner answer   DateTime dateOfBirth   Convert ToDateTime  01 16 1990    var age     DateTime Now - dateOfBirth  Days    365

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The best way that I know of because of leap years and everything is   DateTime birthDate   new DateTime 2000 3 1   int age    int Math Floor  DateTime Now - birthDate  TotalDays   365 25D

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I used ScArcher2 s solution for an accurate Year calculation of a persons age but I needed to take it further and calculate their Months and Days along with the Years       public static Dictionary lt string int gt  CurrentAgeInYearsMonthsDays DateTime  ndtBirthDate  DateTime  ndtReferralDate                  ----------------------------------------------------------------------            Can t determine age if we don t have a dates            ----------------------------------------------------------------------         if  ndtBirthDate    null  return null          if  ndtReferralDate    null  return null           DateTime dtBirthDate   Convert ToDateTime ndtBirthDate           DateTime dtReferralDate   Convert ToDateTime ndtReferralDate              ----------------------------------------------------------------------            Create our Variables           ----------------------------------------------------------------------         Dictionary lt string  int gt  dYMD   new Dictionary lt string int gt             int iNowDate  iBirthDate  iYears  iMonths  iDays          string sDif                  ----------------------------------------------------------------------            Store off current date time and DOB into local variables           ----------------------------------------------------------------------          iNowDate   int Parse dtReferralDate ToString  yyyyMMdd             iBirthDate   int Parse dtBirthDate ToString  yyyyMMdd                ----------------------------------------------------------------------            Calculate Years           ----------------------------------------------------------------------         sDif    iNowDate - iBirthDate  ToString            iYears   int Parse sDif Substring 0  sDif Length - 4               ----------------------------------------------------------------------            Store Years in Return Value           ----------------------------------------------------------------------         dYMD Add  Years   iYears              ----------------------------------------------------------------------            Calculate Months           ----------------------------------------------------------------------         if  dtBirthDate Month  gt  dtReferralDate Month              iMonths   12 - dtBirthDate Month   dtReferralDate Month - 1          else             iMonths   dtBirthDate Month - dtReferralDate Month             ----------------------------------------------------------------------            Store Months in Return Value           ----------------------------------------------------------------------         dYMD Add  Months   iMonths              ----------------------------------------------------------------------            Calculate Remaining Days           ----------------------------------------------------------------------         if  dtBirthDate Day  gt  dtReferralDate Day                Logic  Figure out the days in month previous to the current month  or the admitted month                       Subtract the birthday from the total days which will give us how many days the person has lived since their birthdate day the previous month                       then take the referral date and simply add the number of days the person has lived this month                 If referral date is january  we need to go back to the following year s December to get the days in that month              if  dtReferralDate Month    1                  iDays   DateTime DaysInMonth dtReferralDate Year - 1  12  - dtBirthDate Day   dtReferralDate Day                     else                 iDays   DateTime DaysInMonth dtReferralDate Year  dtReferralDate Month - 1  - dtBirthDate Day   dtReferralDate Day                 else             iDays   dtReferralDate Day - dtBirthDate Day                          ----------------------------------------------------------------------            Store Days in Return Value           ----------------------------------------------------------------------         dYMD Add  Days   iDays            return dYMD

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I would simply do this   DateTime birthDay   new DateTime 1990  05  23   DateTime age   DateTime Now - birthDay    This way you can calculate the exact age of a person  down to the millisecond if you want

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Here s a little code sample for C  I knocked up  be careful around the edge cases specifically leap years  not all the above solutions take them into account  Pushing the answer out as a DateTime can cause problems as you could end up trying to put too many days into a specific month e g  30 days in Feb   public string LoopAge DateTime myDOB  DateTime FutureDate        int years   0      int months   0      int days   0       DateTime tmpMyDOB   new DateTime myDOB Year  myDOB Month  1        DateTime tmpFutureDate   new DateTime FutureDate Year  FutureDate Month  1        while  tmpMyDOB AddYears years  AddMonths months   lt  tmpFutureDate                months            if  months  gt  12                        years                months   months - 12                       if  FutureDate Day  gt   myDOB Day                days   days   FutureDate Day - myDOB Day            else               months--          if  months  lt  0                        years--              months   months   12                    days   days    DateTime DaysInMonth FutureDate AddMonths -1  Year  FutureDate AddMonths -1  Month    FutureDate Day  - myDOB Day                add an extra day if the dob is a leap day     if  DateTime IsLeapYear myDOB Year   amp  amp  myDOB Month    2  amp  amp  myDOB Day    29                  but only if the future date is less than 1st March         if FutureDate  gt   new DateTime FutureDate Year  3 1               days               return  Years      years     Months      months     Days      days

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Common Saying  from months to years old       If you just for common use  here is the code as your information   DateTime today   DateTime Today  DateTime bday   DateTime Parse  2016-2-14    int age   today Year - bday Year  var unit        if  bday  gt  today AddYears -age         age--    if  age    0       Under one year old       age   today Month - bday Month       age   age  lt   0    12   age    age      The next year before birthday      age   today Day - bday Day  gt   0   age   --age      Before the birthday day      unit    month     else       unit    year      if  age  gt  1        unit   unit    s       The test result as below   The birthday  2016-2-14  2016-2-15   gt   age 0  unit month  2016-5-13   gt   age 2  unit months  2016-5-14   gt   age 3  unit months   2016-6-13   gt   age 3  unit months   2016-6-15   gt   age 4  unit months   2017-1-13   gt   age 10  unit months   2017-1-14   gt   age 11  unit months   2017-2-13   gt   age 11  unit months   2017-2-14   gt   age 1  unit year   2017-2-15   gt   age 1  unit year   2017-3-13   gt   age 1  unit year  2018-1-13   gt   age 1  unit year   2018-1-14   gt   age 1  unit year   2018-2-13   gt   age 1  unit year   2018-2-14   gt   age 2  unit years

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The simplest way I ve ever found is this  It works correctly for the US and western europe locales  Can t speak to other locales  especially places like China  4 extra compares  at most  following the initial computation of age   public int AgeInYears DateTime birthDate  DateTime referenceDate      Debug Assert referenceDate  gt   birthDate                   birth date must be on or prior to the reference date       DateTime birth   birthDate Date    DateTime reference   referenceDate Date    int years    reference Year - birth Year              an offset of -1 is applied if the birth date has       not yet occurred in the current year         if  reference Month  gt  birth Month     else if  reference Month  lt  birth Month       --years    else    in birth month         if  reference Day  lt  birth Day        --years         return years       I was looking over the answers to this and noticed that nobody has made reference to regulatory legal implications of leap day births  For instance  per Wikipedia  if you re born on February 29th in various jurisdictions  you re non-leap year birthday varies    In the United Kingdom and Hong Kong  it s the ordinal day of the year  so the next day  March 1st is your birthday  In New Zealand  it s the previous day  February 28th for the purposes of driver licencing  and March 1st for other purposes  Taiwan  it s February 28th    And as near as I can tell  in the US  the statutes are silent on the matter  leaving it up to the common law and to how various regulatory bodies define things in their regulations   To that end  an improvement   public enum LeapDayRule     OrdinalDay       1     LastDayOfMonth   2      static int ComputeAgeInYears DateTime birth  DateTime reference  LeapYearBirthdayRule ruleInEffect      bool isLeapYearBirthday   CultureInfo CurrentCulture Calendar IsLeapDay birth Year  birth Month  birth Day     DateTime cutoff     if  isLeapYearBirthday  amp  amp   DateTime IsLeapYear reference Year           switch  ruleInEffect              case LeapDayRule OrdinalDay          cutoff   new DateTime reference Year  1  1                                AddDays birth DayOfYear - 1           break         case LeapDayRule LastDayOfMonth          cutoff   new DateTime reference Year  birth Month  1                                AddMonths 1                                AddDays -1           break         default          throw new InvalidOperationException                else         cutoff   new DateTime reference Year  birth Month  birth Day          int age    reference Year - birth Year     reference  gt   cutoff   0   -1     return age  lt  0   0   age      It should be noted that this code assumes    A western  European  reckoning of age  and A calendar  like the Gregorian calendar that inserts a single leap day at the end of a month

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I have used the following for this issue  I know it s not very elegant  but it s working   DateTime zeroTime   new DateTime 1  1  1   var date1   new DateTime 1983  03  04   var date2   DateTime Now  var dif   date2 - date1  int years    zeroTime   dif  Year - 1  Log DebugFormat  Years -- gt  0    years

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I have created a SQL Server User Defined Function to calculate someone s age  given their birthdate  This is useful when you need it as part of a query   using System  using System Data  using System Data Sql  using System Data SqlClient  using System Data SqlTypes  using Microsoft SqlServer Server   public partial class UserDefinedFunctions        SqlFunction DataAccess   DataAccessKind Read       public static SqlInt32 CalculateAge string strBirthDate                DateTime dtBirthDate   new DateTime            dtBirthDate   Convert ToDateTime strBirthDate           DateTime dtToday   DateTime Now              get the difference in years         int years   dtToday Year - dtBirthDate Year              subtract another year if we re before the            birth day in the current year         if  dtToday Month  lt  dtBirthDate Month     dtToday Month    dtBirthDate Month  amp  amp  dtToday Day  lt  dtBirthDate Day               years years-1           int intCustomerAge   years          return intCustomerAge

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I ve created an Age struct  which looks like this   public struct Age   IEquatable lt Age gt   IComparable lt Age gt        private readonly int  years      private readonly int  months      private readonly int  days       public int Years    get   return  years          public int Months   get   return  months          public int Days   get   return  days           public Age  int years  int months  int days     this                  years   years           months   months           days   days             public static Age CalculateAge  DateTime dateOfBirth  DateTime date                    Here is some logic that ressembles Mike s solution  although it            also takes into account months  amp  days             Ommitted for brevity          return new Age  years  months  days                 Ommited Equality  Comparable  GetHashCode  functionality for brevity

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The following approach  extract from Time Period Library for  NET class DateDiff  considers the calendar of the culture info      ---------------------------------------------------------------------- private static int YearDiff  DateTime date1  DateTime date2       return YearDiff  date1  date2  DateTimeFormatInfo CurrentInfo Calendar         YearDiff     ---------------------------------------------------------------------- private static int YearDiff  DateTime date1  DateTime date2  Calendar calendar       if   date1 Equals  date2             return 0         int year1   calendar GetYear  date1      int month1   calendar GetMonth  date1      int year2   calendar GetYear  date2      int month2   calendar GetMonth  date2          find the the day to compare   int compareDay   date2 Day    int compareDaysPerMonth   calendar GetDaysInMonth  year1  month1      if   compareDay  gt  compareDaysPerMonth           compareDay   compareDaysPerMonth            build the compare date   DateTime compareDate   new DateTime  year1  month2  compareDay      date2 Hour  date2 Minute  date2 Second  date2 Millisecond      if   date2  gt  date1           if   compareDate  lt  date1               compareDate   compareDate AddYears  1                else         if   compareDate  gt  date1               compareDate   compareDate AddYears  -1                return year2 - calendar GetYear  compareDate         YearDiff   Usage      ---------------------------------------------------------------------- public void CalculateAgeSamples       PrintAge  new DateTime  2000  02  29    new DateTime  2009  02  28            gt  Birthdate 29 02 2000  Age at 28 02 2009 is 8 years   PrintAge  new DateTime  2000  02  29    new DateTime  2012  02  28            gt  Birthdate 29 02 2000  Age at 28 02 2012 is 11 years      CalculateAgeSamples     ---------------------------------------------------------------------- public void PrintAge  DateTime birthDate  DateTime moment       Console WriteLine   Birthdate  0 d   Age at  1 d  is  2  years   birthDate  moment  YearDiff  birthDate  moment           PrintAge

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Here s yet another answer  public static int AgeInYears DateTime birthday  DateTime today        return   today Year - birthday Year    372    today Month - birthday Month    31    today Day - birthday Day     372     This has been extensively unit-tested  It does look a bit  quot magic quot   The number 372 is the number of days there would be in a year if every month had 31 days  The explanation of why it works  lifted from here  is   Let s set Yn   DateTime Now Year  Yb   birthday Year  Mn   DateTime Now Month  Mb   birthday Month  Dn   DateTime Now Day  Db   birthday Day age   Yn - Yb    31  Mn - Mb     Dn - Db     372 We know that what we need is either Yn-Yb if the date has already been reached  Yn-Yb-1 if it has not  a  If Mn lt Mb  we have -341  lt   31  Mn-Mb   lt   -31 and -30  lt   Dn-Db  lt   30 -371  lt   31  Mn - Mb     Dn - Db   lt   -1 With integer division  31  Mn - Mb     Dn - Db     372   -1 b  If Mn Mb and Dn lt Db  we have 31  Mn - Mb    0 and -30  lt   Dn-Db  lt   -1 With integer division  again  31  Mn - Mb     Dn - Db     372   -1 c  If Mn gt Mb  we have 31  lt   31  Mn-Mb   lt   341 and -30  lt   Dn-Db  lt   30 1  lt   31  Mn - Mb     Dn - Db   lt   371 With integer division  31  Mn - Mb     Dn - Db     372   0 d  If Mn Mb and Dn gt Db  we have 31  Mn - Mb    0 and 1  lt   Dn-Db  lt   30 With integer division  again  31  Mn - Mb     Dn - Db     372   0 e  If Mn Mb and Dn Db  we have 31  Mn - Mb    Dn-Db   0 and therefore  31  Mn - Mb     Dn - Db     372   0

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I use this   public static class DateTimeExtensions       public static int Age this DateTime birthDate                return Age birthDate  DateTime Now              public static int Age this DateTime birthDate  DateTime offsetDate                int result 0          result   offsetDate Year - birthDate Year           if  offsetDate DayOfYear  lt  birthDate DayOfYear                          result--                     return result

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I ve made one small change to Mark Soen s answer  I ve rewriten the third line so that the expression can be parsed a bit more easily   public int AgeInYears DateTime bday        DateTime now   DateTime Today      int age   now Year - bday Year                  if  bday AddYears age   gt  now           age--      return age      I ve also made it into a function for the sake of clarity

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Try this solution  it s working   int age    Int32 Parse DateTime Today ToString  yyyyMMdd    -             Int32 Parse birthday ToString  yyyyMMdd rawrrr       10000

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Very simple answer          DateTime dob   new DateTime 1991  3  4            DateTime now   DateTime Now           int dobDay   dob Day  dobMonth   dob Month           int add   -1           if  dobMonth  lt  now Month                        add   0                    else if  dobMonth    now Month                        if dobDay  lt   now Day                                add   0                            else                               add   -1                                  else                       add   -1                     int age   now Year - dob Year   add

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Here is the simplest way to calculate someone s age  Calculating someone s age is pretty straightforward  and here s how  In order for the code to work  you need a DateTime object called BirthDate containing the birthday      C             get the difference in years         int years   DateTime Now Year - BirthDate Year              subtract another year if we re before the            birth day in the current year         if  DateTime Now Month  lt  BirthDate Month                  DateTime Now Month    BirthDate Month  amp  amp               DateTime Now Day  lt  BirthDate Day                years--    VB NET           get the difference in years         Dim years As Integer   DateTime Now Year - BirthDate Year           subtract another year if we re before the           birth day in the current year         If DateTime Now Month  lt  BirthDate Month Or  DateTime Now Month   BirthDate Month And DateTime Now Day  lt  BirthDate Day  Then              years   years - 1         End If

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Here is a function that is serving me well  No calculations   very simple      public static string ToAge this DateTime dob  DateTime  toDate   null                if   toDate HasValue              toDate   DateTime Now          var now   toDate Value           if  now CompareTo dob   lt  0              return  quot Future date quot            int years   now Year - dob Year          int months   now Month - dob Month          int days   now Day - dob Day           if  days  lt  0                        months--              days   DateTime DaysInMonth dob Year  dob Month  - dob Day   now Day                     if  months  lt  0                        years--              months   12   months                      return string Format  quot  0  year s    1  month s    2  days s  quot               years              months              days          And here is a unit test       Test      public void ToAgeTests                 var date   new DateTime 2000  1  1           Assert AreEqual  quot 0 year s   0 month s   1 days s  quot   new DateTime 1999  12  31  ToAge date            Assert AreEqual  quot 0 year s   0 month s   0 days s  quot   new DateTime 2000  1  1  ToAge date            Assert AreEqual  quot 1 year s   0 month s   0 days s  quot   new DateTime 1999  1  1  ToAge date            Assert AreEqual  quot 0 year s   11 month s   0 days s  quot   new DateTime 1999  2  1  ToAge date            Assert AreEqual  quot 0 year s   10 month s   25 days s  quot   new DateTime 1999  2  4  ToAge date            Assert AreEqual  quot 0 year s   10 month s   1 days s  quot   new DateTime 1999  2  28  ToAge date             date   new DateTime 2000  2  15           Assert AreEqual  quot 0 year s   0 month s   28 days s  quot   new DateTime 2000  1  18  ToAge date

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An easy to understand and simple solution     Save today s date  var today   DateTime Today      Calculate the age  var age   today Year - birthdate Year      Go back to the year in which the person was born in case of a leap year if  birthdate Date  gt  today AddYears -age   age--   However  this assumes you are looking for the western idea of the age and not using East Asian reckoning

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private int GetYearDiff DateTime start  DateTime end        int diff   end Year - start Year      if  end DayOfYear  lt  start DayOfYear    diff -  1        return diff     Fact  public void GetYearDiff WhenCalls ShouldReturnCorrectYearDiff           arrange     var now   DateTime Now        act       assert     Assert Equal 24  GetYearDiff new DateTime 1992  7  9   now       passed     Assert Equal 24  GetYearDiff new DateTime 1992  now Month  now Day   now       passed     Assert Equal 23  GetYearDiff new DateTime 1992  12  9   now       passed

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2 Main problems to solve are   1  Calculate Exact age - in years  months  days  etc   2  Calculate Generally perceived age - people usually do not care how old they exactly are  they just care when their birthday in the current year is     Solution for 1 is obvious   DateTime birth   DateTime Parse  1 1 2000    DateTime today   DateTime Today        we usually don t care about birth time TimeSpan age   today - birth            NET FCL should guarantee this as precise double ageInDays   age TotalDays       total number of days     also precise double daysInYear   365 2425           statistical value for 400 years double ageInYears   ageInDays   daysInYear     can be shifted     not so precise     Solution for 2 is the one which is not so precise in determing total age  but is perceived as precise by people  People also usually use it  when they calculate their age  manually    DateTime birth   DateTime Parse  1 1 2000    DateTime today   DateTime Today  int age   today Year - birth Year       people perceive their age in years  if  today Month  lt  birth Month         today Month    birth Month   amp  amp   today Day  lt  birth Day        age--     birthday in current year not yet reached  we are 1 year younger                  no birthday for 29 2  guys     sorry  just wrong date for birth     Notes to 2     This is my preferred solution We cannot use DateTime DayOfYear or TimeSpans  as they shift number of days in leap years I have put there little more lines for readability   Just one more note     I would create 2 static overloaded methods for it  one for universal usage  second for usage-friendliness   public static int GetAge DateTime bithDay  DateTime today          chosen solution method body    public static int GetAge DateTime birthDay        return GetAge birthDay  DateTime Now

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Wow  I had to give my answer here    There are so many answers for such a simple question   private int CalcularIdade DateTime dtNascimento                var nHoje   Convert ToInt32 DateTime Today ToString  yyyyMMdd             var nAniversario   Convert ToInt32 dtNascimento ToString  yyyyMMdd              double diff    nHoje - nAniversario    10000           var ret   Convert ToInt32 Math Truncate diff             return ret

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Just because I don t think the top answer is that clear   public static int GetAgeByLoop DateTime birthday        var age   -1       for  var date   birthday  date  lt  DateTime Today  date   date AddYears 1                 age               return age

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To calculate how many years old a person is    DateTime dateOfBirth   int ageInYears   DateTime Now Year - dateOfBirth Year   if  dateOfBirth  gt  today AddYears -ageInYears    ageInYears --

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With fewer conversions and UtcNow  this code can take care of someone born on the Feb 29 in a leap year   public int GetAge DateTime DateOfBirth        var Now   DateTime UtcNow      return Now Year - DateOfBirth Year -                                         Now Month  gt  DateOfBirth Month                     Now Month    DateOfBirth Month  amp  amp  Now Day  gt   DateOfBirth Day                  0   1

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This is a strange way to do it  but if you format the date to yyyymmdd and subtract the date of birth from the current date then drop the last 4 digits you ve got the age     I don t know C   but I believe this will work in any language   20080814 - 19800703   280111    Drop the last 4 digits   28   C  Code   int now   int Parse DateTime Now ToString  yyyyMMdd     int dob   int Parse dateOfBirth ToString  yyyyMMdd     int age    now - dob    10000    Or alternatively without all the type conversion in the form of an extension method  Error checking omitted   public static Int32 GetAge this DateTime dateOfBirth        var today   DateTime Today       var a    today Year   100   today Month    100   today Day      var b    dateOfBirth Year   100   dateOfBirth Month    100   dateOfBirth Day       return  a - b    10000

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Do we need to consider people who is smaller than 1 year  as Chinese culture  we describe small babies  age as 2 months or 4 weeks    Below is my implementation  it is not as simple as what I imagined  especially to deal with date like 2 28    public static string HowOld DateTime birthday  DateTime now        if  now  lt  birthday          throw new ArgumentOutOfRangeException  birthday must be less than now          TimeSpan diff   now - birthday      int diffDays    int diff TotalDays       if  diffDays  gt  7   year  month and week               int age   now Year - birthday Year           if  birthday  gt  now AddYears -age               age--           if  age  gt  0                        return age    age  gt  1     years      year                      else             month and week             DateTime d   birthday              int diffMonth   1               while  d AddMonths diffMonth   lt   now                                diffMonth                               age   diffMonth-1               if  age    1  amp  amp  d Day  gt  now Day                  age--               if  age  gt  0                                return age    age  gt  1     months      month                              else                               age   diffDays   7                  return age    age  gt  1     weeks      week                                      else if  diffDays  gt  0                int age   diffDays          return age    age  gt  1     days      day              else               int age   diffDays          return  just born             This implementation has passed below test cases    TestMethod  public void TestAge         string age   HowOld new DateTime 2011  1  1   new DateTime 2012  11  30        Assert AreEqual  1 year   age        age   HowOld new DateTime 2011  11  30   new DateTime 2012  11  30        Assert AreEqual  1 year   age        age   HowOld new DateTime 2001  1  1   new DateTime 2012  11  30        Assert AreEqual  11 years   age        age   HowOld new DateTime 2012  1  1   new DateTime 2012  11  30        Assert AreEqual  10 months   age        age   HowOld new DateTime 2011  12  1   new DateTime 2012  11  30        Assert AreEqual  11 months   age        age   HowOld new DateTime 2012  10  1   new DateTime 2012  11  30        Assert AreEqual  1 month   age        age   HowOld new DateTime 2008  2  28   new DateTime 2009  2  28        Assert AreEqual  1 year   age        age   HowOld new DateTime 2008  3  28   new DateTime 2009  2  28        Assert AreEqual  11 months   age        age   HowOld new DateTime 2008  3  28   new DateTime 2009  3  28        Assert AreEqual  1 year   age        age   HowOld new DateTime 2009  1  28   new DateTime 2009  2  28        Assert AreEqual  1 month   age        age   HowOld new DateTime 2009  2  1   new DateTime 2009  3  1        Assert AreEqual  1 month   age           NOTE         new DateTime 2008  1  31  AddMonths 1     new DateTime 2009  2  28          new DateTime 2008  1  28  AddMonths 1     new DateTime 2009  2  28       age   HowOld new DateTime 2009  1  31   new DateTime 2009  2  28        Assert AreEqual  4 weeks   age        age   HowOld new DateTime 2009  2  1   new DateTime 2009  2  28        Assert AreEqual  3 weeks   age        age   HowOld new DateTime 2009  2  1   new DateTime 2009  3  1        Assert AreEqual  1 month   age        age   HowOld new DateTime 2012  11  5   new DateTime 2012  11  30        Assert AreEqual  3 weeks   age        age   HowOld new DateTime 2012  11  1   new DateTime 2012  11  30        Assert AreEqual  4 weeks   age        age   HowOld new DateTime 2012  11  20   new DateTime 2012  11  30        Assert AreEqual  1 week   age        age   HowOld new DateTime 2012  11  25   new DateTime 2012  11  30        Assert AreEqual  5 days   age        age   HowOld new DateTime 2012  11  29   new DateTime 2012  11  30        Assert AreEqual  1 day   age        age   HowOld new DateTime 2012  11  30   new DateTime 2012  11  30        Assert AreEqual  just born   age        age   HowOld new DateTime 2000  2  29   new DateTime 2009  2  28        Assert AreEqual  8 years   age        age   HowOld new DateTime 2000  2  29   new DateTime 2009  3  1        Assert AreEqual  9 years   age        Exception e   null       try               age   HowOld new DateTime 2012  12  1   new DateTime 2012  11  30              catch  ArgumentOutOfRangeException ex                e   ex             Assert IsTrue e    null       Hope it s helpful

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Another function  not by me but found on the web and refined it a bit   public static int GetAge DateTime birthDate        DateTime n   DateTime Now     To avoid a race condition around midnight     int age   n Year - birthDate Year       if  n Month  lt  birthDate Month     n Month    birthDate Month  amp  amp  n Day  lt  birthDate Day           age--       return age      Just two things that come into my mind  What about people from countries that do not use the Gregorian calendar  DateTime Now is in the server-specific culture I think  I have absolutely zero knowledge about actually working with Asian calendars and I do not know if there is an easy way to convert dates between calendars  but just in case you re wondering about those Chinese guys from the year 4660  -

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Just use    DateTime Now - myDate  TotalHours   8766 0   The current date - myDate   TimeSpan  get total hours and divide in the total hours per year and get exactly the age months days

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I have no knowledge about DateTime but all I can do is this  using System                       public class Program       public static int getAge int month  int day  int year            DateTime today   DateTime Today          int currentDay   today Day          int currentYear   today Year          int currentMonth   today Month          int age   0          if  currentMonth  lt  month                age -  1            else if  currentMonth    month                if  currentDay  lt  day                    age -  1                                  currentYear -  year          age    currentYear          return age            public static void Main                 int ageInYears   getAge 8  10  2007           Console WriteLine ageInYears            A little confusing  but looking at the code more carefully  it will all make sense

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Simple Code   var birthYear 1993   var age   DateTime Now AddYears -birthYear  Year

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I think the TimeSpan has all that we need in it  without having to resort to 365 25  or any other approximation   Expanding on Aug s example   DateTime myBD   new DateTime 1980  10  10   TimeSpan difference   DateTime Now Subtract myBD    textBox1 Text   difference Years     years     difference Months     Months     difference Days     days

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I think this problem can be solved with an easier way like this- The class can be like- using System   namespace TSA       class BirthDay               double ageDay          public BirthDay int day  int month  int year                        DateTime birthDate   new DateTime year  month  day               ageDay    birthDate - DateTime Now  TotalDays    DateTime UtcNow                    internal int GetAgeYear                         return  int Math Truncate ageDay   365                      internal int GetAgeMonth                         return  int Math Truncate  ageDay   365    30                      And calls can be like- BirthDay b   new BirthDay 1 12 1990   int year   b GetAgeYear    int month   b GetAgeMonth

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private int GetAge int  year  int  month  int  day       DateTime yourBirthDate  new DateTime  year   month   day        DateTime todaysDateTime   DateTime Today      int noOfYears   todaysDateTime Year - yourBirthDate Year       if  DateTime Now Month  lt  yourBirthDate Month             DateTime Now Month    yourBirthDate Month  amp  amp  DateTime Now Day  lt  yourBirthDate Day                 noOfYears--             return  noOfYears

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Here is a very simple and easy to follow example    private int CalculateAge       get birthdate    DateTime dtBirth   Convert ToDateTime BirthDatePicker Value      int byear   dtBirth Year     int bmonth   dtBirth Month     int bday   dtBirth Day     DateTime dtToday   DateTime Now     int tYear   dtToday Year     int tmonth   dtToday Month     int tday   dtToday Day     int age   tYear - byear     if  bmonth  lt  tmonth         age--     else if  bmonth    tmonth  amp  amp  bday gt tday              age--       return age

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TimeSpan diff   DateTime Now - birthdayDateTime  string age   String Format   0  y  years   0  M  months   0  d   days old   diff     I m not sure how exactly you d like it returned to you  so I just made a readable string

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This classic question is deserving of a Noda Time solution   static int GetAge LocalDate dateOfBirth        Instant now   SystemClock Instance Now          The target time zone is important         It should align with the  current physical location  of the person        you are talking about   When the whereabouts of that person are unknown         then you use the time zone of the person who is  asking  for the age         The time zone of birth is irrelevant       DateTimeZone zone   DateTimeZoneProviders Tzdb  America New York         LocalDate today   now InZone zone  Date       Period period   Period Between dateOfBirth  today  PeriodUnits Years        return  int  period Years      Usage   LocalDate dateOfBirth   new LocalDate 1976  8  27   int age   GetAge dateOfBirth     You might also be interested in the following improvements    Passing in the clock as an IClock  instead of using SystemClock Instance  would improve testability  The target time zone will likely change  so you d want a DateTimeZone parameter as well    See also my blog post on this subject  Handling Birthdays  and Other Anniversaries

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I want to add Hebrew calendar calculations  or other System Globalization calendar can be used in the same way    using rewrited functions from this thread   Public Shared Function CalculateAge BirthDate As DateTime  As Integer     Dim HebCal As New System Globalization HebrewCalendar        Dim now   DateTime Now       Dim iAge   HebCal GetYear now  - HebCal GetYear BirthDate      Dim iNowMonth   HebCal GetMonth now   iBirthMonth   HebCal GetMonth BirthDate      If iNowMonth  lt  iBirthMonth Or  iNowMonth   iBirthMonth AndAlso HebCal GetDayOfMonth now   lt  HebCal GetDayOfMonth BirthDate   Then iAge -  1     Return iAge End Function

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This is simple and appears to be accurate for my needs  I am making an assumption for the purpose of leap years that regardless of when the person chooses to celebrate the birthday they are not technically a year older until 365 days have passed since their last birthday  i e 28th February does not make them a year older   DateTime now   DateTime Today  DateTime birthday   new DateTime 1991  02  03    3rd feb  int age   now Year - birthday Year   if  now Month  lt  birthday Month     now Month    birthday Month  amp  amp  now Day  lt  birthday Day    not had bday this year yet   age--   return age

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public string GetAge this DateTime birthdate  string ageStrinFormat   null        var date   DateTime Now AddMonths -birthdate Month  AddDays -birthdate Day       return string Format ageStrinFormat      0   1   2             date Year - birthdate Year   date Month  date Day

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This is not a direct answer  but more of a philosophical reasoning about the problem at hand from a quasi-scientific point of view   I would argue that the question does not specify the unit nor culture in which to measure age  most answers seem to assume an integer annual representation  The SI-unit for time is second  ergo the correct generic answer should be  of course assuming normalized DateTime and taking no regard whatsoever to relativistic effects    var lifeInSeconds    DateTime Now Ticks - then Ticks  TickFactor    In the Christian way of calculating age in years   var then          Then  in this case the birthday var now   DateTime UtcNow  int age   now Year - then Year  if  now AddYears -age   lt  then  age--    In finance there is a similar problem when calculating something often referred to as the Day Count Fraction  which roughly is a number of years for a given period  And the age issue is really a time measuring issue   Example for the actual actual  counting all days  correctly   convention   DateTime start  end           Whatever  assume start is before end  double startYearContribution   1 -  double  start DayOfYear    double   DateTime IsLeapYear start Year    366   365   double endYearContribution    double end DayOfYear    double  DateTime IsLeapYear end Year    366   365   double middleContribution    double   end Year - start Year - 1    double DCF   startYearContribution   endYearContribution   middleContribution    Another quite common way to measure time generally is by  serializing   the dude who named this date convention must seriously have been trippin     DateTime start  end           Whatever  assume start is before end int days    end - start  Days    I wonder how long we have to go before a relativistic age in seconds becomes more useful than the rough approximation of earth-around-sun-cycles during one s lifetime so far    Or in other words  when a period must be given a location or a function representing motion for itself to be valid

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This gives  more detail  to this question  Maybe this is what you re looking for  DateTime birth   new DateTime 1974  8  29   DateTime today   DateTime Now  TimeSpan span   today - birth  DateTime age   DateTime MinValue   span      Make adjustment due to MinValue equalling 1 1 1 int years   age Year - 1  int months   age Month - 1  int days   age Day - 1      Print out not only how many years old they are but give months and days as well Console Write   0  years   1  months   2  days   years  months  days

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It can be this simple   int age   DateTime Now AddTicks 0 - dob Ticks  Year - 1

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This is the easiest way to answer this in a single line  DateTime Dob   DateTime Parse  quot 1985-04-24 quot      int Age   DateTime MinValue AddDays DateTime Now Subtract Dob  TotalHours 24 - 1  Year - 1   This also works for leap years

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Here is a test snippet   DateTime bDay   new DateTime 2000  2  29   DateTime now   new DateTime 2009  2  28   MessageBox Show string Format  Test  0   1   2                    CalculateAgeWrong1 bDay  now           outputs 9                 CalculateAgeWrong2 bDay  now           outputs 9                 CalculateAgeCorrect bDay  now          outputs 8                 CalculateAgeCorrect2 bDay  now         outputs 8   Here you have the methods   public int CalculateAgeWrong1 DateTime birthDate  DateTime now        return new DateTime now Subtract birthDate  Ticks  Year - 1     public int CalculateAgeWrong2 DateTime birthDate  DateTime now        int age   now Year - birthDate Year       if  now  lt  birthDate AddYears age           age--       return age     public int CalculateAgeCorrect DateTime birthDate  DateTime now        int age   now Year - birthDate Year       if  now Month  lt  birthDate Month     now Month    birthDate Month  amp  amp  now Day  lt  birthDate Day           age--       return age     public int CalculateAgeCorrect2 DateTime birthDate  DateTime now        int age   now Year - birthDate Year          For leap years we need this     if  birthDate  gt  now AddYears -age            age--         Don t use         if  birthDate AddYears age   gt  now              age--       return age

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My suggestion  int age    int    DateTime Now - bday  TotalDays 365 242199     That seems to have the year changing on the right date   I spot tested up to age 107

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I have a customized method to calculate age  plus a bonus validation message just in case it helps   public void GetAge DateTime dob  DateTime now  out int years  out int months  out int days        years   0      months   0      days   0       DateTime tmpdob   new DateTime dob Year  dob Month  1       DateTime tmpnow   new DateTime now Year  now Month  1        while  tmpdob AddYears years  AddMonths months   lt  tmpnow                months            if  months  gt  12                        years                months   months - 12                       if  now Day  gt   dob Day          days   days   now Day - dob Day      else               months--          if  months  lt  0                        years--              months   months   12                    days    DateTime DaysInMonth now AddMonths -1  Year  now AddMonths -1  Month    now Day - dob Day             if  DateTime IsLeapYear dob Year   amp  amp  dob Month    2  amp  amp  dob Day    29  amp  amp  now  gt   new DateTime now Year  3  1           days           private string ValidateDate DateTime dob    This method will validate the date       int Years   0  int Months   0  int Days   0       GetAge dob  DateTime Now  out Years  out Months  out Days        if  Years  lt  18          message    Years     is too young  Please try again on your 18th birthday        else if  Years  gt   65          message   Years     is too old  Date of Birth must not be 65 or older        else         return null    Denotes validation passed     Method call here and pass out datetime value  MM dd yyyy if server set to USA locale   Replace this with anything a messagebox or any container to display   DateTime dob   DateTime Parse  03 10 1982       string message   ValidateDate dob    lbldatemessage Visible    StringIsNullOrWhitespace message   lbldatemessage Text   message          Ternary if message is null then default to empty string   Remember you can format the message any way you like

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This is one of the most accurate answers that is able to resolve the birthday of 29th of Feb compared to any year of 28th Feb   public int GetAge DateTime birthDate        int age   DateTime Now Year - birthDate Year       if  birthDate DayOfYear  gt  DateTime Now DayOfYear          age--       return age

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Keeping it simple  and possibly stupid      DateTime birth   new DateTime 1975  09  27  01  00  00  00   TimeSpan ts   DateTime Now - birth  Console WriteLine  You are approximately     ts TotalSeconds ToString       seconds old

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I ve spent some time working on this and came up with this to calculate someone s age in years  months and days  I ve tested against the Feb 29th problem and leap years and it seems to work  I d appreciate any feedback   public void LoopAge DateTime myDOB  DateTime FutureDate        int years   0      int months   0      int days   0       DateTime tmpMyDOB   new DateTime myDOB Year  myDOB Month  1        DateTime tmpFutureDate   new DateTime FutureDate Year  FutureDate Month  1        while  tmpMyDOB AddYears years  AddMonths months   lt  tmpFutureDate                months             if  months  gt  12                        years                months   months - 12                       if  FutureDate Day  gt   myDOB Day                days   days   FutureDate Day - myDOB Day            else               months--           if  months  lt  0                        years--              months   months   12                     days                DateTime DaysInMonth                  FutureDate AddMonths -1  Year  FutureDate AddMonths -1  Month                 FutureDate Day - myDOB Day                add an extra day if the dob is a leap day     if  DateTime IsLeapYear myDOB Year   amp  amp  myDOB Month    2  amp  amp  myDOB Day    29                  but only if the future date is less than 1st March         if  FutureDate  gt   new DateTime FutureDate Year  3  1               days

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var birthDate          DOB var resultDate   DateTime Now - birthDate    Using resultDate you can apply TimeSpan properties whatever you want to display it

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SQL version   declare  dd smalldatetime    1980-04-01  declare  age int   YEAR GETDATE   -YEAR  dd  if   dd gt  DATEADD YYYY  - age  GETDATE     set  age    age -1  print  age

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Here s a one-liner   int age   new DateTime DateTime Now Subtract birthday  Ticks  Year-1

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How about this solution    static string CalcAge DateTime birthDay        DateTime currentDate   DateTime Now               int approximateAge   currentDate Year - birthDay Year      int daysToNextBirthDay    birthDay Month   30   birthDay Day  -           currentDate Month   30   currentDate Day         if  approximateAge    0    approximateAge    1                                int month    Math Abs daysToNextBirthDay   30           int days   Math Abs daysToNextBirthDay   30            if  month    0              return  Your age is      daysToNextBirthDay     days            return  Your age is      month     months and     days     days                if  daysToNextBirthDay  gt  0          return  Your age is      --approximateAge     Years        return  Your age is      approximateAge     Years

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How come the MSDN help did not tell you that  It looks so obvious    System DateTime birthTime   AskTheUser myUser       -  System DateTime now   System DateTime Now  System TimeSpan age   now - birthTime     As simple as that double ageInDays   age TotalDays     Will you convert to whatever you want yourself

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Here is a solution   DateTime dateOfBirth   new DateTime 2000  4  18   DateTime currentDate   DateTime Now   int ageInYears   0  int ageInMonths   0  int ageInDays   0   ageInDays   currentDate Day - dateOfBirth Day  ageInMonths   currentDate Month - dateOfBirth Month  ageInYears   currentDate Year - dateOfBirth Year   if  ageInDays  lt  0        ageInDays    DateTime DaysInMonth currentDate Year  currentDate Month       ageInMonths   ageInMonths--       if  ageInMonths  lt  0                ageInMonths    12          ageInYears--           if  ageInMonths  lt  0        ageInMonths    12      ageInYears--     Console WriteLine   0    1    2    ageInYears  ageInMonths  ageInDays

[c#] How do I calculate someone's age based on a DateTime type birthday?

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