PHP Cookbook

3.5. Finding the Difference of Two Dates

Problem

You want to find the elapsed time between two dates. For example, you want to tell a user how long it’s been since she last logged onto your site.

Solution

Convert both dates to epoch timestamps and subtract one from the other. Use this code to separate the difference into weeks, days, hours, minutes, and seconds:

// 7:32:56 pm on May 10, 1965
$epoch_1 = mktime(19,32,56,5,10,1965);
// 4:29:11 am on November 20, 1962
$epoch_2 = mktime(4,29,11,11,20,1962);

$diff_seconds  = $epoch_1 - $epoch_2;
$diff_weeks    = floor($diff_seconds/604800);
$diff_seconds -= $diff_weeks   * 604800;
$diff_days     = floor($diff_seconds/86400);
$diff_seconds -= $diff_days    * 86400;
$diff_hours    = floor($diff_seconds/3600);
$diff_seconds -= $diff_hours   * 3600;
$diff_minutes  = floor($diff_seconds/60);
$diff_seconds -= $diff_minutes * 60;

print "The two dates have $diff_weeks weeks, $diff_days days, ";
print "$diff_hours hours, $diff_minutes minutes, and $diff_seconds ";
print "seconds elapsed between them.";
The two dates have 128 weeks, 6 days, 14 hours, 3 minutes, 
               and 45 seconds elapsed between them.

Note that the difference isn’t divided into larger chunks than weeks (i.e., months or years) because those chunks have variable length and wouldn’t give an accurate count of the time difference calculated.

Discussion

There are a few strange things going on here that you should be aware of. First of all, 1962 and 1965 precede the beginning of the epoch. Fortunately, mktime( ...