How do i know the safe days in my menstruation cycle?

Know your cycle: The average cycle pattern is 28 days with ovulation occurring around day 14. You are most fertile shortly before ovulation and this time should be avoided to prevent pregnancy. Consider the number of days between your cycles. A good rule is to assume you will ovulate 14 days after the first day of your last cycle. Also, you can use a condom at anytime to prevent pregnancy and stds.