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[2015-12-31 11:56 UTC] ruben at solunapilates dot es
Description:
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In day 31 of December, the function date('F',strtotime('- 1 month')); returns "December" instead November. Happens all months
Test script:
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$today=date('F',strtotime('- 1 month'));
print($today);
Expected result:
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November
Actual result:
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December
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Last updated: Fri Oct 31 02:00:02 2025 UTC |
That just happens on months with more days than previous month on the last day. December 31 - 1 month = November 31 => December 1 Better try date('F',strtotime('first day of last month')), which will give you what you expect.By that logic, date('Y', strtotime('-1 year', strtotime('2016-02-29'))) should return 2012 because 2015-02-29 doesn't exist.Of course not, 2016/02/29 - a year would be 2015/03/01. This is how UNIX date math works. You can try the original issue from your Linux shell prompt: % date --date='-1 month' +'Last month was %B?' Last month was December? Or in sqlite: sqlite> select datetime('2015-12-31', '-1 month'); 2015-12-01 00:00:00 See this for some extra background: http://www.gnu.org/software/tar/manual/html_node/Relative-items-in-date-strings.html#SEC120 PHP is consistent with GNU tools and the many other tools using this standard approach. In the end there is no right answer when you are subtracting a fuzzy concept such as a year or a month. Take this, for example: php > echo date('Y/m/d', strtotime('-1 month', strtotime('2015/12/31'))); 2015/12/01 php > echo date('Y/m/d', strtotime('-1 month', strtotime('2015/12/30'))); 2015/11/30 By your logic these should both return the same day? That doesn't make much sense. Having 31-n == 30-n would make doing math on timestamps and comparing results really difficult if 31-n was not greater than 30-n. UNIX chooses mathematical consistency at the timestamp level. Mapping these timestamps to a display date is where things get interesting and you have to take this into account when you apply fuzzy concepts like months and years to timestamps.