In the terms of payment form, when using payment method as cutoff days, in some localization, there's a field called additional months, so that the due date can be calculated no only in the current month, but based on the cutoff days and adding months.

examples:

without using additional months functionality:

if we have a terms of payment ( Net 60 days from the end of the calendar Month), so if today us April 23 and cutoff day is 15 the due date will be May15th.

with using additional months functionality:

if we have a terms of payment ( Net 60 days from the end of the calendar Month), so if today us April 23,cutoff day is 15 and additional months of 1 the due date will be June 15th.