Keep track of the days of the menstrual cycle
  • Before relying on this method, a woman records the number of days in each menstrual cycle for at least 6 months. The first day of monthly bleeding is always counted as day 1.
Estimate the fertile time
  • The woman subtracts 18 from the length of her shortest recorded cycle. This tells her the estimated rst day of her fertile time. Then she subtracts 11 days from the length of her longest recorded cycle. This tells her the estimated last day of her fertile time.
Avoid unprotected sex during fertile time
  • The couple avoids vaginal sex, or uses condoms or a diaphragm, during the fertile time. They can also use withdrawal or spermicides, but these are less effective.
Update calculations monthly
  • She updates these calculations each month, always using the 6 most recent cycles.

    Example:

    • If the shortest of her last 6 cycles was 27 days, 27 – 18 = 9. She starts avoiding unprotected sex on day 9.

    • If the longest of her last 6 cycles was 31 days, 31 – 11 = 20. She can have unprotected sex again on day 21.

    • Thus, she must avoid unprotected sex from day 9 through day 20 of her cycle.

Calendar indicating days when to avoid sex or use another method on days 9-20