IMPORTANT: A woman can use the Standard Days Method if most of her menstrual cycles are 26 to 32 days long. If she has more than 2 longer or shorter cycles within a year, the Standard Days Method will be less effective and she may want to choose another method.
Keep track of the days of the menstrual cycle
A woman keeps track of the days of her menstrual cycle, counting the first day of monthly bleeding as day 1.
Avoid unprotected sex on days 8–19
Days 8 through 19 of every cycle are considered fertile days for all users of the Standard Days Method.
The couple avoids vaginal sex or uses condoms or a diaphragm during days 8 through 19. They can also use withdrawal or spermicides, but these are less effective.
The couple can have unprotected sex on all the other days of the cycle—days 1 through 7 at the beginning of the cycle and from day 20 until her next monthly bleeding begins.
Use memory aids if needed
The couple can use CycleBeads, a color-coded string of beads that indicates fertile and nonfertile days of a cycle, or they can mark a calendar or use some other memory aid.
Calendar Rhythm Method
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 first 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.
