Hormonal birth control is heralded as the simple solution for controlling fertility, but it's not for every woman. Women who have religious objections to contraception, who have hormonal sensitivities, who have certain kinds of cancers or who prefer natural and alternative medicines need to rely on other methods of preventing pregnancy. For these women, natural family planning methods, like the calendar method, can help pinpoint fertile days, so women can avoid pregnancy without medication.
Step 1
Record your menstrual cycle on the first day of your period. Mark this on your calender as day one, and circle it. Number each day in your cycle, circling days when you're on your period. The next time you get your period, start over, recording that as day one.
Step 2
Record your cycle days for at least three months. The longer you record your cycle length, the more accurate the calendar method will be. Recording your cycle for at least six months to a year is the preferred method, according to the University of California, Santa Barbara's SexInfo.com.
Step 3
Read over your cycle data, and pick out the longest and shortest cycles. Subtract 18 days from your shortest cycle to get the cycle day that marks the beginning of your fertile period. For example, if your shortest cycle was 28 days, the 10th day of your cycle marks when your fertile days begin.
Step 4
Subtract 11 days from your longest cycle to determine the end of your fertile period. For example, if your longest cycle was 33 days, your fertile period will end on day 22.
Step 5
Avoid intercourse or use a backup pregnancy prevention method, like condoms or spermicide, during this window. In the example, the fertile window begins at cycle day 10 and ends at day 22.
