Many items may come to mind when thinking about birth control, but a calendar usually isn't one of them. However, using a calendar to identify days of the woman's menstrual cycle when she is fertile and abstaining from sexual intercourse during that time can be an effective way of preventing pregnancy. Although the process takes almost an entire year before it is most effective, the lack of side effects and natural approach to birth control makes it an appealing choice for many women.
Step 1
Use the calendar as a written record of each menstrual cycle. The first day of menstrual bleeding should count as the first day of the menstrual cycle. Keep recording each menstrual cycle in this manner until approximately eight to 12 months have passed.
Step 2
Look through the calendar and identify the longest and shortest menstrual cycles. Make a note of how many days the longest cycle was as well as how many the shortest cycle was.
Step 3
Subtract 18 from the number of days of the shortest menstrual cycle. For example, if the shortest menstrual cycle was 28 days, subtracting 18 from this number would equal the number 10. This number is the first day of the menstrual cycle that you may be fertile.
Step 4
Subtract 11 from the number of days of the longest menstrual cycle. For example, if the longest menstrual cycle was 31 days, subtracting 11 from this number would equal the number 20. This number is the last day of the menstrual cycle that you may be fertile.
Step 5
Note the fertile time frame of the menstrual cycle. The time between the first day that you may be fertile to the last day that may be fertile is the time of the menstrual cycle when pregnancy is possible and sexual intercourse should be avoided.
Step 6
Continue adding data for each subsequent menstrual cycle and re-calculate the fertile time period. Once there is more 12 months worth of data present, ignore the data from the oldest cycle and only use the previous 12 months for calculation purposes.
Tips and Warnings
- The effectiveness of this method increases when analyzing signs of fertility in addition to using the calendar. Monitoring cervical fluid, basal body temperature and cervical position can indicate when a woman is fertile and give confirmation that the fertile time found using the calendar method is correct. If total abstinence during the fertile period is not possible, using a backup method of birth control during this time is an option.
- Planned Parenthood states that 9 percent of couples who use this method perfectly will still become pregnant. The calendar method of birth control is generally easiest for women who have very regular menstrual cycles, explains the American Pregnancy Association.
Things You'll Need
- Calendar
