PHP Manual Function Reference Date and Time Related Extensions Date/Time DateTimeImmutable DateTimeImmutable::add DateTimeImmutable DateTimeImmutable::__construct DateTimeImmutable::add (PHP 5 >= 5.5.0)DateTimeImmutable::add — Adds an amount of days, months, years, hours, minutes and seconds Description public DateTimeImmutable DateTimeImmutable::add ( DateInterval $interval ) Like DateTime::add() but works with DateTimeImmutable.