Code Examples -> Comparing Dates

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PHP Code Examples

Title :	Comparing Dates
Categories :	PHP, Date Time	Justin French
Date :	May 05th 2003
Grade :	5 of 5 (graded 6 times)
Viewed :	13357
File :	No file for this code example.
Images :	No Images for this code example.

Search :	More code by Justin French
Action :	Grade This Code Example
Tools :	My Examples List

Code

PHP has got some awesome functions working with dates... it's just a little daunting to know which
ones to use at first.

IMHO, the easiest way to work with dates is if they're in Unix timestamp format (total number of
seconds since the Unix epoch (Jan 1, 1970)).

You can also get a timestamp for "now" on the server using time()

So, first thing we need to do is take your existing date, and get it into a timestamp.

You might have dates in many formats:
YYYY-MM-DD
YY-MM-DD
MM-DD-YY
MM/DD/YY
MM-DD-YYYY
MM/DD/YYYY
DD-MM-YY
DD-MM-YYYY
DD/MM/YY
DD/MM/YYYY
Or even something natural language like 'December 10, 2002'

PHP's strtotime() function takes a wide variety of natural language and date formates, converting
them to timestamps.

<?php
$stamp = strtotime('2003-04-28');
$stamp = strtotime('last month');
?>

In my experience, you need to test what sort of results you get with strtotime, depending on your
format. strtotime() is a little bit US-centric, so it doesn't work with DD/MM/YY formats at all.
You need to switch the day and month around:

<?php
$nonUSdate = '27/06/77';
list($day,$month,$year) = explode('/',$nonUSdate);
$newDate = "{$month}/{$day}/{$year}";
$stamp = strtotime($newDate);
?>

You can read more about strtotime(), with plenty of examples at
http://www.weberdev.com/strtotime

Now that you can convert your dates to timestamps, it's really easy to compare them:

<?php
$date1 = strtotime('06/27/1977');
$date2 = strtotime('12/18/2003');

if($date1 > $date2) { ... }
if($date1 < time()) { ... }
if($date2 >= $date1) { ... }
?>

It's also really easy to add, subtract or divide by days/hours/minutes

There are 60 seconds in a minute, 60 minutes in an hour, and 24 hours in a day = 86400seconds

<?php
// add an hour to a stamp
$date1 = $date1 + 3600;

// subtract a week
$date1 = $date1 - 2073600;
?>

Best of all, PHP's date() function accepts unix timestamps as it's second argument, so you easily
make the timestamps human-readable again:

<?php
echo date('Y-m-d',$mystamp);
?>

Check out these pages for more info, and do some experimenting:

http://www.weberdev.com/date
http://www.weberdev.com/strtotime
http://www.weberdev.com/time
http://www.weberdev.com/explode

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User Comments

	Jos� Santos wrote : 966 It`s very useful in PHP, and it`s used in somme mutch Websites and Intranet`s ! I have question: how do you calculate 2073600 ? I say that a minute have 60 seconds, a hour 60 minutes and, a day 24 hours. But I dont get this result !!
	mick 28 wrote :967 60 seconds = 1 minute 3600 seconds = 1 hour (60 minutes) 86400 seconds = 1 day (24 hours) 604800 seconds = 1 week (7 days) 2419200 seconds = 1 Lunar Month (28 days) Guess it`s been a long week for Justin :-)