How to calculate safe period / fertile period

• Find the last period start date
• Find out shortest and longest period cycles by observing your period cycles for atleast 6 months
• Illustrative example of calculating fertile period
• shortest cycle=27 days
• longest cycle=28 days
• Subtract 18 days from the shortest cycle 27-18=9 days
• Subtract 10 days from the longest cycle 28-10=18 days
• The 9^th day to 18 ^th day from your last period is the unsafe period
• The rest is the safe period