The calendar method is a natural method of birth control. It means that you won’t have intercourse on the days the girl is most likely to get pregnant, which is mid-cycle.
You figure out the fertile days and abstain from intercourse during this period.
The fertile period is different for every girl. So you have to make a calculation to know what days you might be fertile.
The period of abstinence spans quite some days before and after ovulation because ovulation can be earlier or later than expected and because sperm in a girl’s body can remain active for a week.
It’s an extremely unreliable method if you want to prevent pregnancy. But if you long for a child, it helps you to know which days of the month you are most likely to get pregnant.

How to make this calculation?
Pros & cons