How do I calculate someone s age in Java

Question

I want to return an age in years as an int in a Java method  What I have now is the following where getBirthDate   returns a Date object  with the birth date  -     public int getAge         long ageInMillis   new Date   getTime   - getBirthDate   getTime         Date age   new Date ageInMillis        return age getYear        But since getYear   is deprecated I m wondering if there is a better way to do this  I m not even sure this works correctly  since I have no unit tests in place  yet

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If you are using GWT you will be limited to using java util Date  here is a method that takes the date as integers  but still uses java util Date   public int getAge int year  int month  int day        Date now   new Date        int nowMonth   now getMonth   1      int nowYear   now getYear   1900      int result   nowYear - year       if  month  gt  nowMonth            result--            else if  month    nowMonth            int nowDay   now getDate             if  day  gt  nowDay                result--                      return result

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Compute from string date in the format of yyyy-MM-dd HH mm ss the age of a person      author Yaron Ronen     date 04 06 2012       private int computeAge String sDate           Initial variables      Date dbDate   null      SimpleDateFormat dateFormat   new SimpleDateFormat  yyyy-MM-dd HH mm ss                  Parse sDate      try               dbDate    Date dateFormat parse sDate             catch ParseException e                Log e  MyApplication   Can not compute age from date   sDate e           return ILLEGAL DATE     Const   -2               Compute age      long timeDiff   System currentTimeMillis   - dbDate getTime              int age    int  timeDiff   MILLI SECONDS YEAR       MILLI SECONDS YEAR   31558464000L       return age

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The fields birth and effect are both date fields       Calendar bir   Calendar getInstance    bir setTime birth   int birthNm   bir get Calendar DAY OF YEAR   int birthYear   bir get Calendar YEAR   Calendar eff   Calendar getInstance    eff setTime effect     This basically a modification of John O s solution without using depreciated methods  I spent a fair amount of time trying to get his code to work in in my code  Maybe this will save others that time

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Modern answer and overview  a  Java-8  java time-package   LocalDate start   LocalDate of 1996  2  29   LocalDate end   LocalDate of 2014  2  28      use for age-calculation  LocalDate now   long years   ChronoUnit YEARS between start  end   System out println years      17   Note that the expression LocalDate now   is implicitly related to the system timezone  which is often overlooked by users   For clarity it is generally better to use the overloaded method now ZoneId of  Europe Paris    specifying an explicit timezone  here  Europe Paris  as example   If the system timezone is requested then my personal preference is to write LocalDate now ZoneId systemDefault    to make the relation to the system timezone clearer  This is more writing effort but makes reading easier   b  Joda-Time  Please note that the proposed and accepted Joda-Time-solution yields a different computation result for the dates shown above  a rare case   namely   LocalDate birthdate   new LocalDate 1996  2  29   LocalDate now   new LocalDate 2014  2  28      test  in real world without args Years age   Years yearsBetween birthdate  now   System out println age getYears        18   I consider this as a small bug but the Joda-team has a different view on this weird behaviour and does not want to fix it  weird because the day-of-month of end date is smaller than of start date so the year should be one less   See also this closed issue   c  java util Calendar etc   For comparison see the various other answers  I would not recommend using these outdated classes at all because the resulting code is still errorprone in some exotic cases and or way too complex considering the fact that the original question sounds so simple  In year 2015 we have really better libraries   d  About Date4J   The proposed solution is simple but will sometimes fail in case of leap years  Just evaluating the day of year is not reliable   e  My own library Time4J   This works similar to Java-8-solution  Just replace LocalDate by PlainDate and ChronoUnit YEARS by CalendarUnit YEARS  However  getting  today  requires an explicit timezone reference   PlainDate start   PlainDate of 1996  2  29   PlainDate end   PlainDate of 2014  2  28      use for age-calculation  today         gt  end   SystemClock inZonalView EUROPE PARIS  today       or in system timezone  end   SystemClock inLocalView   today    long years   CalendarUnit YEARS between start  end   System out println years      17

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Try to copy this one in your code  then use the method to get the age   public static int getAge Date birthday        GregorianCalendar today   new GregorianCalendar        GregorianCalendar bday   new GregorianCalendar        GregorianCalendar bdayThisYear   new GregorianCalendar         bday setTime birthday       bdayThisYear setTime birthday       bdayThisYear set Calendar YEAR  today get Calendar YEAR         int age   today get Calendar YEAR  - bday get Calendar YEAR        if today getTimeInMillis    lt  bdayThisYear getTimeInMillis            age--       return age

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Check out Joda  which simplifies date time calculations  Joda is also the basis of the new standard Java date time apis  so you ll be learning a soon-to-be-standard API     EDIT  Java 8 has something very similar and is worth checking out   e g    LocalDate birthdate   new LocalDate  1970  1  20   LocalDate now   new LocalDate    Years age   Years yearsBetween birthdate  now     which is as simple as you could want  The pre-Java 8 stuff is  as you ve identified  somewhat unintuitive

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I use this piece of code for age calculation  Hope this helps   no libraries used  private static DateFormat dateFormat   new SimpleDateFormat  yyyy-MM-dd   Locale getDefault      public static int calculateAge String date         int age   0      try           Date date1   dateFormat parse date           Calendar now   Calendar getInstance            Calendar dob   Calendar getInstance            dob setTime date1           if  dob after now                 throw new IllegalArgumentException  Can t be born in the future                      int year1   now get Calendar YEAR           int year2   dob get Calendar YEAR           age   year1 - year2          int month1   now get Calendar MONTH           int month2   dob get Calendar MONTH           if  month2  gt  month1                age--            else if  month1    month2                int day1   now get Calendar DAY OF MONTH               int day2   dob get Calendar DAY OF MONTH               if  day2  gt  day1                    age--                                catch  ParseException e            e printStackTrace              return age

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JDK 8 makes this easy and elegant   public class AgeCalculator        public static int calculateAge LocalDate birthDate  LocalDate currentDate            if   birthDate    null   amp  amp   currentDate    null                 return Period between birthDate  currentDate  getYears              else               return 0                      A JUnit test to demonstrate its use    public class AgeCalculatorTest         Test     public void testCalculateAge Success                setup         LocalDate birthDate   LocalDate of 1961  5  17              exercise         int actual   AgeCalculator calculateAge birthDate  LocalDate of 2016  7  12               assert         Assert assertEquals 55  actual             Everyone should be using JDK 8 by now  All earlier versions have passed the end of their support lives

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This Method is unit tested properly for very different cases       taking care of Leap Year days difference in a year      and date cases month and Year boundary cases  12 31 1980  01 01 1980 etc       public static int getAge Date dateOfBirth         Calendar today   Calendar getInstance        Calendar birthDate   Calendar getInstance         int age   0       birthDate setTime dateOfBirth       if  birthDate after today             throw new IllegalArgumentException  Can t be born in the future               age   today get Calendar YEAR  - birthDate get Calendar YEAR           If birth date is greater than todays date  after 2 days adjustment of leap year  then decrement age one year        if    birthDate get Calendar DAY OF YEAR  - today get Calendar DAY OF YEAR   gt  3                  birthDate get Calendar MONTH   gt  today get Calendar MONTH              age--           If birth date and todays date are of same month and birth day of month is greater than todays day of month then decrement age      else if   birthDate get Calendar MONTH     today get Calendar MONTH     amp  amp                 birthDate get Calendar DAY OF MONTH   gt  today get Calendar DAY OF MONTH              age--             return age

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public int getAge Date dateOfBirth         Calendar now   Calendar getInstance        Calendar dob   Calendar getInstance         dob setTime dateOfBirth        if  dob after now                  throw new IllegalArgumentException  Can t be born in the future               int age   now get Calendar YEAR  - dob get Calendar YEAR        if  now get Calendar DAY OF YEAR   lt  dob get Calendar DAY OF YEAR                  age--             return age

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public int getAge String birthdate  String today          birthdate    1986-02-22         today    2014-09-16          String class has a split method for splitting a string        split  lt delimiter gt          birth 0    1986 as string        birth 1    02 as string        birth 2    22 as string        now 0    2014 as string        now 1    09 as string        now 2    16 as string          birth   and   now   arrays are automatically contains 3 elements         split method here returns 3 elements because of yyyy-MM-dd value     String birth     birthdate split  -        String now     today split  -        int age   0          let us convert string values into integer values        with the use of Integer parseInt  lt string gt       int ybirth   Integer parseInt birth 0        int mbirth   Integer parseInt birth 1        int dbirth   Integer parseInt birth 2         int ynow   Integer parseInt now 0        int mnow   Integer parseInt now 1        int dnow   Integer parseInt now 2         if ybirth  lt  ynow      has age if birth year is lesser than current year         age   ynow - ybirth     let us get the interval of birth year and current year         if mbirth    mnow      when birth month comes  it s ok to have age   ynow - ybirth if             if dbirth  gt  dnow     birth day is coming  need to subtract 1 from age  not yet a bday                 age--           else if mbirth  gt  mnow   age--       birth month is comming  need to subtract 1 from age                        return age

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With the date4j library    int age   today getYear   - birthdate getYear    if today getDayOfYear    lt  birthdate getDayOfYear       age   age - 1

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Calendar now   Calendar getInstance    Calendar dob   Calendar getInstance    dob setTime       if  dob after now       throw new IllegalArgumentException  Can t be born in the future      int year1   now get Calendar YEAR   int year2   dob get Calendar YEAR   int age   year1 - year2  int month1   now get Calendar MONTH   int month2   dob get Calendar MONTH   if  month2  gt  month1      age--    else if  month1    month2      int day1   now get Calendar DAY OF MONTH     int day2   dob get Calendar DAY OF MONTH     if  day2  gt  day1        age--           age is now correct

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I simply use the milliseconds in a year constant value to my advantage   Date now   new Date    long timeBetween   now getTime   - age getTime    double yearsBetween   timeBetween   3 15576e 10  int age    int  Math floor yearsBetween

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I appreciate all correct answers but this is the kotlin answer for the same question  I hope would be helpful to kotlin developers   fun calculateAge birthDate  Date   Int           val now   Date           val timeBetween   now getTime   - birthDate getTime            val yearsBetween   timeBetween   3 15576e 10          return Math floor yearsBetween  toInt

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import java time LocalDate  import java time ZoneId  import java time Period   public class AgeCalculator1        public static void main String args              LocalDate start   LocalDate of 1970  2  23           LocalDate end   LocalDate now ZoneId systemDefault              Period p   Period between start  end             The output of the program is             45 years 6 months and 6 days          System out print p getYears       year     p getYears    gt  1    s                     System out print p getMonths       month     p getMonths    gt  1    s and       and               System out print p getDays       day     p getDays    gt  1    s  n       n             method main ends here

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With Java 8  we can calculate a person age with one line of code   public int calCAge int year  int month int days                    return LocalDate now   minus Period of year  month  days   getYear

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The correct answer using JodaTime is   public int getAge         Years years   Years yearsBetween new LocalDate getBirthDate     new LocalDate         return years getYears        You could even shorten it into one line if you like  I copied the idea from BrianAgnew s answer  but I believe this is more correct as you see from the comments there  and it answers the question exactly

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This is an improved version of the one above    considering that you want age to be an  int   because sometimes you don t want to fill your program with a bunch of libraries   public int getAge Date dateOfBirth        int age   0      Calendar born   Calendar getInstance        Calendar now   Calendar getInstance        if dateOfBirth   null            now setTime new Date             born setTime dateOfBirth             if born after now                 throw new IllegalArgumentException  Can t be born in the future                      age   now get Calendar YEAR  - born get Calendar YEAR                        if now get Calendar DAY OF YEAR   lt  born get Calendar DAY OF YEAR                  age- 1                        return age

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String dateofbirth has the date of birth  and format is whatever  defined in the following line    org joda time format DateTimeFormatter formatter    org joda time format DateTimeFormat forPattern  mm dd yyyy      Here is how to format   org joda time DateTime birthdateDate   formatter parseDateTime dateofbirth    org joda time DateMidnight birthdate   new         org joda time DateMidnight birthdateDate getYear    birthdateDate getMonthOfYear    birthdateDate getDayOfMonth      org joda time DateTime now   new org joda time DateTime    org joda time Years age   org joda time Years yearsBetween birthdate  now   java lang String ageStr   java lang String valueOf  age getYears       Variable ageStr will have the years

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It s perhaps surprising to note that you don t need to know how many days or months there are in a year or how many days are in those months  likewise  you don t need to know about leap years  leap seconds  or any of that stuff using this simple  100  accurate method   public static int age Date birthday  Date date        DateFormat formatter   new SimpleDateFormat  yyyyMMdd        int d1   Integer parseInt formatter format birthday        int d2   Integer parseInt formatter format date        int age    d2-d1  10000      return age

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import java io     class AgeCalculator       public static void main String args                  InputStreamReader ins new InputStreamReader System in           BufferedReader hey new BufferedReader ins            try                       System out println  Please enter your name                  String name hey readLine                 System out println  Please enter your birth date                  String date hey readLine                 System out println  please enter your birth month                 String month hey readLine                 System out println  please enter your birth year                 String year hey readLine                 System out println  please enter current year                 String cYear hey readLine                 int bDate   Integer parseInt date               int bMonth   Integer parseInt month               int bYear   Integer parseInt year               int ccYear Integer parseInt cYear                int age               age   ccYear-bYear              int totalMonth 12              int yourMonth totalMonth-bMonth               System out println   Hi     name     your are     age     years     yourMonth     months old                       catch IOException err                        System out println

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Elegant  seemingly correct  timestamp difference based  variant of Yaron Ronen solution   I am including a unit test to prove when and why it is not correct  It is impossible due  to possibly  different number of leap days  and seconds  in any timestamp difference  The discrepancy should be max  -1 day  and one second  for this algorithm  see test2    whereas Yaron Ronen solution based on completely constant assumption of timeDiff   MILLI SECONDS YEAR can differ 10 days for a 40ty year old  nevertheless this variant is incorrect too   It is tricky  because this improved variant  using formula diffAsCalendar get Calendar YEAR  - 1970  returns correct results most of the time  as number of leap years in on average same between two dates          Compute person s age based on timestamp difference between birth date and given date    and prove it is INCORRECT approach      public class AgeUsingTimestamps    public int getAge Date today  Date dateOfBirth        long diffAsLong   today getTime   - dateOfBirth getTime        Calendar diffAsCalendar   Calendar getInstance        diffAsCalendar setTimeInMillis diffAsLong       return diffAsCalendar get Calendar YEAR  - 1970     base time where timestamp 0  precisely 1 1 1970 00 00 00         final static DateFormat df   new SimpleDateFormat  dd MM yyy HH mm ss          Test     public void test1   throws Exception           Date dateOfBirth   df parse  10 1 2000 00 00 00            assertEquals 87  getAge df parse  08 1 2088 23 59 59    dateOfBirth            assertEquals 87  getAge df parse  09 1 2088 23 59 59    dateOfBirth            assertEquals 88  getAge df parse  10 1 2088 00 00 01    dateOfBirth                Test     public void test2   throws Exception              between 2000 and 2021 was 6 leap days            but between 1970  base time  and 1991 there was only 5 leap days            therefore age is switched one day earlier                See http   www onlineconversion com leapyear htm         Date dateOfBirth   df parse  10 1 2000 00 00 00            assertEquals 20  getAge df parse  08 1 2021 23 59 59    dateOfBirth            assertEquals 20  getAge df parse  09 1 2021 23 59 59    dateOfBirth       ERROR  returns incorrect age 21 here         assertEquals 21  getAge df parse  10 1 2021 00 00 01    dateOfBirth

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What about this one   public Integer calculateAge Date date        if  date    null            return null            Calendar cal1   Calendar getInstance        cal1 setTime date       Calendar cal2   Calendar getInstance        int i   0      while  cal1 before cal2             cal1 add Calendar YEAR  1           i    1            return i

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public int getAge Date birthDate        Calendar a   Calendar getInstance Locale US       a setTime date       Calendar b   Calendar getInstance Locale US       int age   b get YEAR  - a get YEAR       if  a get MONTH   gt  b get MONTH      a get MONTH     b get MONTH   amp  amp  a get DATE   gt  b get DATE              age--            return age

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Easiest way without any libraries       long today   new Date   getTime        long diff   today - birth      long age   diff   DateUtils YEAR IN MILLIS

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public class CalculateAge     private int age   private void setAge int age        this age age     public void calculateAge Date date        Calendar calendar Calendar getInstance         Calendar calendarnow Calendar getInstance             calendarnow getTimeZone         calendar setTime date        int getmonth  calendar get calendar MONTH        int getyears  calendar get calendar YEAR        int currentmonth  calendarnow get calendarnow MONTH        int currentyear  calendarnow get calendarnow YEAR        int age     currentyear 12 currentmonth - getyears 12 getmonth   12       setAge age     public int getAge         return this age

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Here is the java code to calculate age in year  month and days    public static AgeModel calculateAge long birthDate        int years   0      int months   0      int days   0       if  birthDate    0              create calendar object for birth day         Calendar birthDay   Calendar getInstance            birthDay setTimeInMillis birthDate              create calendar object for current day         Calendar now   Calendar getInstance            Calendar current   Calendar getInstance              Get difference between years         years   now get Calendar YEAR  - birthDay get Calendar YEAR              get months         int currMonth   now get Calendar MONTH    1          int birthMonth   birthDay get Calendar MONTH    1             Get difference between months         months   currMonth - birthMonth             if month difference is in negative then reduce years by one and calculate the number of months          if  months  lt  0                years--              months   12 - birthMonth   currMonth            else if  months    0  amp  amp  now get Calendar DATE   lt  birthDay get Calendar DATE                 years--              months   11                       Calculate the days         if  now get Calendar DATE   gt  birthDay get Calendar DATE               days   now get Calendar DATE  - birthDay get Calendar DATE           else if  now get Calendar DATE   lt  birthDay get Calendar DATE                 int today   now get Calendar DAY OF MONTH               now add Calendar MONTH  -1               days   now getActualMaximum Calendar DAY OF MONTH  - birthDay get Calendar DAY OF MONTH    today            else               days   0              if  months    12                    years                    months   0                                       Create new Age object     return new AgeModel days  months  years

[java] How do I calculate someone's age in Java?

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