Bug #79452 [Opn]: DateTime::diff() generates months differently between time zones

Edit report at https://bugs.php.net/bug.php?id=79452&edit=1 ID: 79452 Updated by: cmb@php.net Reported by: corey dot taylor dot fl at gmail dot com Summary: DateTime::diff() generates months differently between time zones Status: Open Type: Bug Package: Date/time related PHP Version: 7.4.4 Block user comment: N Private report: N New Comment: Before the actual diff is calculated, the DateTime objects are converted to UTC; doing this in PHP shows the problem[1]. [1] <https://3v4l.org/gBtjX#v720> Previous Comments: ------------------------------------------------------------------------ [2020-04-06 01:22:43] corey dot taylor dot fl at gmail dot com Description: ------------ If you create DateTime instances in 'America/New_York' or 'UTC' time zone and compare them using DateTime::diff() the months value is different than using DateTime instances in 'Europe/Berlin' or 'Asia/Tokyo'. date_default_timezone_set('America/New_York'); $from = new DateTime('2019-06-01'); $to = new DateTime('2019-10-01'); var_dump($from->diff($to)->m); -- int(4) date_default_timezone_set('Asia/Tokyo'); $from = new DateTime('2019-06-01'); $to = new DateTime('2019-10-01'); var_dump($from->diff($to)->m); -- int(3) The generated days value is the same for both. If this isn't determined to be an implementation error, then can the exepcation be documented for DateTime::diff()? Right now, it's impossible to tell how the DateTime objects are compared between time zones. Expected result: ---------------- The generated difference in months is the same for 2 dates is the same regardless of the time zone they are in. ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=79452&edit=1