DateTime plus 1 month will return wrong date

Asked Dec 01 '20 at 15:08

Active Dec 02 '20 at 08:28

Viewed 144 times

I stumbled upon this today:

If I substract 1 month and 1 day from today's date I get 2020-10-31 and if I reverse this, so I add 1 month and 1 day back to the original date then I should get todays date, but I get tomorrows date instead.

$now=DateTime::createFromFormat('Y-m-d', '2020-12-01');
$now->sub(new DateInterval('P1M1D'));
$now->add(new DateInterval('P1M1D'));
echo($now->format('Y-m-d')); \\ prints 2020-12-02
assert($now->format('Y-m-d')=='2020-12-01'); \\Fails

Does anyone have an explanation for this and how could I avoid getting the wrong date back?

Edit

The code itself is useless as it is. This issue was caught by one of my unit tests. The test is checking how many days are between the current date and a given date minus P1M1D. This test got 1 instead of 0 yesterday.
I tried to use different ways to get the day like strtotime('-1 month -1 day') and DateTime's modify method

Edit 2

I actually found this exact issue on stackoverflow (have no idea how I didn't find it yesterday)this answer answers my question in detail.

edited Dec 02 '20 at 08:28

asked Dec 01 '20 at 15:08

mxsxs2

Don't subtract/add a day? Movements from the end of of the month is wonky due to the number of days each month. It's best to do it from the start of the month. – aynber Dec 01 '20 at 15:10
Why do you need to reverse it? You already have your original date. – El_Vanja Dec 01 '20 at 15:13
What have you tried to debug the problem? – Nico Haase Dec 01 '20 at 17:00
Please see edit. – mxsxs2 Dec 02 '20 at 08:20

DateTime plus 1 month will return wrong date

0 Answers0