We also wrote our own function that handles it. Although, it's purely by random chance that we discovered the problem. It's not something we would specifically have tested for.  I wonder how many other people are using it in production with no idea that it's a problem.

I also confirmed this. This is pretty serious, too! There are an infinite number of examples in which you can reproduce it; here are a few:


  //  expect 06-15-2008, get 06-22-2008
  $date = strtotime('3 Sunday June 2008');
  echo date('m-d-Y', $date);
  
  //  expect 07-08-2008, get 07-15-2008
  $date = strtotime('2 Tuesday July 2008');
  echo date('m-d-Y', $date);
  
  //  expect 08-22-2008, get 08-29-2008
  $date = strtotime('4 Friday August 2008');
  echo date('m-d-Y', $date);
  
  //  expect 09-29-2008, get 10-06-2008
  $date = strtotime('5 Monday September 2008');
  echo date('m-d-Y', $date);
  
  //  expect 10-01-2008, get 10-08-2008
  $date = strtotime('1 Wednesday October 2008');
  echo date('m-d-Y', $date);


Developers please take note: THIS IS A SERIOUS BUG! (and it's been around for a long time)

Derick, please take another look at this.

I've examined it in some depth, and tend to agree there's a bug here.  However, if you read the GNU Date Input Formats syntax, linked from http://php.net/manual/function.strtotime.php, very closely, you find it says:

"a day of the week will forward the date (only if necessary) to reach that day of the week in the future"

... and ...

"a number may precede a day of the week item to move forward supplementary weeks."

The crucial word here is "supplementary". Taken together, these specifications suggest that, somewhat counter-intuitively:

   Monday month year

should represent the first Monday of the month, no matter what date it falls on, and

   1 Monday month year

should be the Monday *after* that (i.e. the 2nd Monday!!), and so on. Other wording in the GNU Date "Day of week items" section would tend to confirm this interpretation.

I therefore submit that the bug actually manifests when the first occurrence of the requested weekday falls on any date *other* than the first of the month! :(

However you interpret it, it's nonetheless clear that the relationship of "1 weekday" to "weekday" should be fixed -- either according to the GNU specification to occur 1 week later, or more intuitively to mean the same thing. It's definitely NOT right that "1 Monday" (for example) means something different from "Monday" *only* when "Monday" is the 1st of the month...!!

Assigning this to myself, but be aware that we do not necessarily implement this GNU date stuff -- we've never done this either. I'll check it though.

Then there's a doc problem, because currently http://php.net/strtotime describes its first argument as "The string to parse, according to the GNU ? Date Input Formats syntax", with a link to the GNU documentation.  If strtotime() does not, in fact, implement the entirety of what's described there, exactly as described, then what's actually implemented should be incorporated into the PHP manual and that link removed.

Yeah, and I've done some work on that -- but it's not ready yet.

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.

Sorry to re-open, I found the same bug on:
PHP Version 5.2.6-pl6-gentoo

Some code to reproduce:
<?php
echo date('Y-m-d', strtotime('first Monday', mktime(0, 0, 0, 12, 1, 2008)));
?>

Shows 2008-12-08, while indeed the first Monday in December is 2008-12-01.

I had second thoughts about the "timestamp" passed into strtotime(), so I tried to create the date in a slightly different way but it failed never the less.

I can also confirm this on 5.2.6_2 on FreeBSD.

Additional code:

Works:
<?php
// 2008-12-02
echo date('Y-m-d', strtotime('first Tuesday December 2008'));
?>

Does not:
<?php
// 2008-12-08
echo date('Y-m-d', strtotime('first Monday December 2008'));
?>

Confirmed it broken in 5.2.7-dev as well.

Since it appears to be fixed in 5.3-alpha3-dev, is there any chance this fix can be backported?

Derick, feedback was given..

Derick, this bug has obviously been fixed in PHP_5_2. As it has been 
a bugfix why isn't it committed to PHP_5_2?!

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.

I merged this last weekend, so closing.

I stumbled onto this while searching for an answer. I'm using PHP v7.2.33 and am seeing this error.

echo date('Y-m-d', strtotime('first Thursday October 2020')); echo "<br>";
echo date('Y-m-d', strtotime('first Friday October 2020')); echo "<br>";

2020-10-08
2020-10-02