[php] How to find out what the date was 5 days ago?

Well, the following returns what date was 5 days ago:

$days_ago = date('Y-m-d', mktime(0, 0, 0, date("m") , date("d") - 5, date("Y")));

But, how do I find what was 5 days ago from any date, not just today?

For example: What was 5 days prior to 2008-12-02?

Try this

$date = date("Y-m-d", strtotime("-5 day"));

define('SECONDS_PER_DAY', 86400);
$days_ago = date('Y-m-d', time() - 5 * SECONDS_PER_DAY);

Other than that, you can use strtotime for any date:

$days_ago = date('Y-m-d', strtotime('January 18, 2034') - 5 * SECONDS_PER_DAY);

Or, as you used, mktime:

$days_ago = date('Y-m-d', mktime(0, 0, 0, 12, 2, 2008) - 5 * SECONDS_PER_DAY);

Well, you get it. The key is to remove enough seconds from the timestamp.

find out what the date was 5 days ago from today in php

$date = strtotime(date("Y-m-d", strtotime("-5 day")));

find out what the date was n days ago from today in php

$date = strtotime(date("Y-m-d", strtotime("-n day")));

General algorithms for date manipulation convert dates to and from Julian Day Numbers. Here is a link to a description of such algorithms, a description of the best algorithms currently known, and the mathematical proofs of each of them: http://web.archive.org/web/20140910060704/http://mysite.verizon.net/aesir_research/date/date0.htm

Use the built in date_sub and date_add functions to math with dates. (See http://php.net/manual/en/datetime.sub.php)

Similar to Sazzad's answer, but in procedural style PHP,

$date = date_create('2008-12-02');
date_sub($date, date_interval_create_from_date_string('5 days'));
echo date_format($date, 'Y-m-d'); //outputs 2008-11-27

simple way to find the same is

$date = date("Y-m-d", strtotime('-5 days', strtotime('input_date')));

Simply do this...hope it help

$fifteendaysago = date_create('15 days ago');
echo date_format($fifteendaysago, 'Y-m-d');

5 days ago from a particular date:

$date = new DateTime('2008-12-02');
$date->sub(new DateInterval('P5D'));
echo $date->format('Y-m-d') . "\n";

If you want a method in which you know the algorithm, or the functions mentioned in the previous answer aren't available: convert the date to Julian Day number (which is a way of counting days from January 1st, 4713 B.C), then subtract five, then convert back to calendar date (year, month, day). Sources of the algorithms for the two conversions is section 9 of http://www.hermetic.ch/cal_stud/jdn.htm or http://en.wikipedia.org/wiki/Julian_day