How to add 30 days in date in php?

Do not use php's date[] function, it's not as accurate as the below solution and furthermore it is unreliable in the future.

Use the DateTime class

The reason you should avoid anything to do with UNIX timestamps [time[], date[], strtotime[] etc] is that they will inevitably break in the year 2038 due to integer limitations.

The maximum value of an integer is 2147483647 which converts to Tuesday, 19 January 2038 03:14:07 so come this time; this minute; this second; everything breaks

Source

Another example of why I stick to using DateTime is that it's actually able to calculate months correctly regardless of what the current date is:

$now = strtotime['31 December 2019'];

for [$i = 1; $i