Subtracting months may not work as you might expect. Code shows how subtracting 2 months from consecutive days produces potentially unexpected results. <?php$origin = date_create('2025-01-31T00:00:00');$target = date_create('2024-11-26T00:00:00');$interval = date_diff($origin, $target);echo "interval total days: ".$interval->format('%a days');echo "interval object years: ".$interval->format('%y years');echo "interval object months: ".$interval->format('%m months');echo "interval object days: ".$interval->format('%d days');$d1 = date_create('2025-01-31T00:00:00');$d2 = date_create('2025-02-01T00:00:00');$d3 = date_create('2025-02-02T00:00:00');$d1->add($interval);$d2->add($interval);$d3->add($interval);echo "Add (negative) interval object to each date. Non-consecutive results: ";echo($d1->format("Y-m-d\TH:i:s"));echo($d2->format("Y-m-d\TH:i:s"));echo($d3->format("Y-m-d\TH:i:s"));$d1 = date_create('2025-01-31T00:00:00');$d2 = date_create('2025-02-01T00:00:00');$d3 = date_create('2025-02-02T00:00:00');$d1->sub(new DateInterval('P'.$interval->format('%a').'D'));$d2->sub(new DateInterval('P'.$interval->format('%a').'D'));$d3->sub(new DateInterval('P'.$interval->format('%a').'D'));echo "Use same dates, but subtract total number of days instead of adding interval object. Results (consecutive): ";echo($d1->format("Y-m-d\TH:i:s"));echo($d2->format("Y-m-d\TH:i:s"));echo($d3->format("Y-m-d\TH:i:s"));$d1 = date_create('2025-01-31T00:00:00');$d2 = date_create('2025-02-01T00:00:00');$d3 = date_create('2025-02-02T00:00:00');echo "Do month separately (interesting): ";echo ('Subtract '. $interval->format('%m').' months (might not expect this):');echo ('Jan 31 - 2 months (61 days = Dec, 31 days + Nov, 30 days) ==> Dec 1');echo ('Feb 1 - 2 months (62 days = Dec, 31 days + Jan, 31 days) ==> Dec 1');$d1->sub(new DateInterval('P'.$interval->format('%m').'M'));echo $d1->format("Y-m-d\TH:i:s");$d2->sub(new DateInterval('P'.$interval->format('%m').'M'));echo $d2->format("Y-m-d\TH:i:s");$d3->sub(new DateInterval('P'.$interval->format('%m').'M'));echo $d3->format("Y-m-d\TH:i:s");?>Output: interval total days: 66 daysinterval object years: 0 yearsinterval object months: 2 monthsinterval object days: 5 dayscreate 3 dates that are consecutive, but in two months:$d1 = 2025-01-31T00:00:00$d2 = 2025-02-01T00:00:00$d3 = 2025-02-02T00:00:00Add (negative) interval object to each date. Non-consecutive results:2024-11-26T00:00:002024-11-26T00:00:002024-11-27T00:00:00Use same dates, but subtract total number of days instead of adding interval object. Results (consecutive):2024-11-26T00:00:002024-11-27T00:00:002024-11-28T00:00:00Do month separately (interesting):Subtract 2 months (might not expect this):Jan 31 - 2 months (61 days = Dec, 31 days + Nov, 30 days) ==> Dec 1Feb 1 - 2 months (62 days = Dec, 31 days + Jan, 31 days) ==> Dec 12024-12-01T00:00:002024-12-01T00:00:002024-12-02T00:00:00