Earned Leave issue, it starts from 0, but how it adds end of the month? only for a month or starting to now?

If I make a leave type with earned leave, leave of 30 days a year, now every month it will add 2.5days.
but after assigning to 01-01-2021 to 31-12-2021 period, at the month of February it shows 0, where my time started from January and that January month is missing, now the end of February, will it add both January and February (5days) or only for February(2.5days) ?