Here is some example code to reproduce the problem:

<?php

$timestamp = gmmktime(12, 0, 0, 12, 28, 1992);
echo 'Week number for ' . gmdate('D M d, Y H:i:s', $timestamp) . ': ' . gmdate('W', $timestamp) . '<br>';

$timestamp = gmmktime(12, 0, 0, 12, 29, 1992);
echo 'Week number for ' . gmdate('D M d, Y H:i:s', $timestamp) . ': ' . gmdate('W', $timestamp) . '<br>';

$timestamp = gmmktime(12, 0, 0, 12, 30, 1992);
echo 'Week number for ' . gmdate('D M d, Y H:i:s', $timestamp) . ': ' . gmdate('W', $timestamp) . '<br>';

$timestamp = gmmktime(12, 0, 0, 12, 31, 1992);
echo 'Week number for ' . gmdate('D M d, Y H:i:s', $timestamp) . ': ' . gmdate('W', $timestamp) . '<br>';

$timestamp = gmmktime(12, 0, 0, 12, 28, 2020);
echo 'Week number for ' . gmdate('D M d, Y H:i:s', $timestamp) . ': ' . gmdate('W', $timestamp) . '<br>';

$timestamp = gmmktime(12, 0, 0, 12, 29, 2020);
echo 'Week number for ' . gmdate('D M d, Y H:i:s', $timestamp) . ': ' . gmdate('W', $timestamp) . '<br>';

$timestamp = gmmktime(12, 0, 0, 12, 30, 2020);
echo 'Week number for ' . gmdate('D M d, Y H:i:s', $timestamp) . ': ' . gmdate('W', $timestamp) . '<br>';

$timestamp = gmmktime(12, 0, 0, 12, 31, 2020);
echo 'Week number for ' . gmdate('D M d, Y H:i:s', $timestamp) . ': ' . gmdate('W', $timestamp) . '<br>';

?>

Expected result:

Week number for Mon Dec 28, 1992 12:00:00: 53
Week number for Tue Dec 29, 1992 12:00:00: 53
Week number for Wed Dec 30, 1992 12:00:00: 53
Week number for Thu Dec 31, 1992 12:00:00: 53
Week number for Mon Dec 28, 2020 12:00:00: 53
Week number for Tue Dec 29, 2020 12:00:00: 53
Week number for Wed Dec 30, 2020 12:00:00: 53
Week number for Thu Dec 31, 2020 12:00:00: 53

Actual result:

Week number for Mon Dec 28, 1992 12:00:00: 1
Week number for Tue Dec 29, 1992 12:00:00: 1
Week number for Wed Dec 30, 1992 12:00:00: 1
Week number for Thu Dec 31, 1992 12:00:00: 1
Week number for Mon Dec 28, 2020 12:00:00: 1
Week number for Tue Dec 29, 2020 12:00:00: 1
Week number for Wed Dec 30, 2020 12:00:00: 1
Week number for Thu Dec 31, 2020 12:00:00: 1

Check http://www.timeanddate.com/calendar/custom.html?year=1992&month=12&typ=1&display=1&wno=1 and http://www.timeanddate.com/calendar/custom.html?year=2020&month=12&typ=1&display=1&wno=1 to see these expected results confirmed.

Sorry for the bulky post, but this way there is no room for misinterpretation.

Thanks,

Paul van der Maas
---
www.stunning-stuff.com

Indeed a bug, will have a look at it - thanks for the reproducable case.

Thanks for your quick reply and thanks for doing such a great job on PHP. You dev's really make this the best open source language today.

I hope you are able to solve this problem (I'm sure you will). One more note though: This problem should reoccur every 28 years before and after 1992. This might help you in your testing.

Thanks,

Paul van der Maas
---
www.stunning-stuff.com

This bug has been fixed in CVS.

Snapshots of the sources are packaged every three hours; this change
will be in the next snapshot. You can grab the snapshot at
http://snaps.php.net/.
 
Thank you for the report, and for helping us make PHP better.

date('W', $timestamp) fails to return "01" for some January 1st years on PHP version 5.3.2 and 5.2.8 on CentOS and Windows.


$year = 1970;
$month = 1;
$day = 1;

while ($year <= 2028) {
  $timestamp = mktime(12, 0, 0, $month, $day, $year);
  print $year . " :: " . date('W', $timestamp). " :: " . date('D', $timestamp) . "\n</br>";
  $year++;
}

Expect 01 for every year
but instead get
1970 :: 01 :: Thu
1971 :: 53 :: Fri
1972 :: 52 :: Sat
1973 :: 01 :: Mon
1974 :: 01 :: Tue
1975 :: 01 :: Wed
1976 :: 01 :: Thu
1977 :: 53 :: Sat
1978 :: 52 :: Sun
...
2020 :: 01 :: Wed
2021 :: 53 :: Fri
2022 :: 52 :: Sat
2023 :: 52 :: Sun
2024 :: 01 :: Mon
2025 :: 01 :: Wed
2026 :: 01 :: Thu
2027 :: 53 :: Fri
2028 :: 52 :: Sat

1st falling on Friday returns 53 
1st falling on Saturday/Sunday return 52


Checked dates using
http://www.tuxgraphics.org/toolbox/cal_year.html


Warwick Shaw

Hi Warwick,

The 1st week of a year does not necessarily start on the first of January 
under the rules of ISO8601. I checked your examples and they seemed fine. 
Please read up on ISO8601.

-Paul

Hi,

I have the same problem using date('W') to show week number of 13/June/2010 which should be 25, but it displays 23.

I use php 5.2.6 through WAMP2.

This is the first time I hear about snapshot so not sure what am I suppose to do to fix this problem.

Can someone please explain to me what should I do?

Thank you,

Sigal

23 is the correct week number according to timeanddate.com. Remember the week 
number is determined using ISO8601 rules!!

Btw, a snapshot release is an 'overnight' release of the latest version of a 
software package. Google will tell you more.

-Paul

Hello,

it seems that this bug is still alive:-). My tries to calculate the week for timestamps belonging to 31 December 2012 are returning the wrong result as can be seen here:

date('Y/W', 1356908400)         => 2012/01
date('Y/m/d H:i:s', 1356908400) => 2012/12/31 00:00:00

Calls with timestamps belonging to 30/12/12 or 01/01/13 result in the correct output. 

Expected behavior (for me reading the ISO 8601 doc) would be to have the year 2013 in the first call to the date function.

I'm using debian wheezy (testing) with the following php version:
PHP 5.4.4-13 (cli) (built: Feb 19 2013 10:54:11)

Thanks and cheers,
Angel Tchorbadjiiski