My girlfriend menstruates on the 8th of this month, and it is normal every month. When will you come next month? How to calculate? Why do I always remember wrong? ...
A good memory is better than a bad writing. The best way to remember is to mark on the calendar, when to start, how much money, and when to end, at a glance. The exact date depends on how many days your girlfriend's cycle is. If it's 28 days, it's the 6th of next month; if it's 30 days, it's the 8th of next month.