Calendar

The calendar method attempts to predict ovulation using a woman's menstrual history. By keeping a written record of each cycle, you can determine when you're least likely to conceive.

Effectiveness rate. The typical effectiveness rate among users of the calendar method is 87 percent. This means that 13 out of 100 women practicing this method for one year will get pregnant. The calendar method isn't dependable if your cycles vary in length.

Side effects and health risks. The downside of using the calendar method is the requirement for prolonged abstinence or use of barrier methods and the need to monitor your cycle for several months before using the method. This method doesn't protect against STDs.

How to use the calendar method. If you decide to use the calendar method, you'll calculate which days you're likely to become pregnant. During that time, abstain from sex or use barrier methods. Here are some tips for using this method:

• Keep a record of the number of days in each cycle, counting from the first day of one period to the first day of the next period. When bleeding starts, circle that day.
• Check your record of previous months, find the shortest cycle and subtract 18 from the total number of days. For example, if your shortest cycle is 26 days, 26 - 18 = 8.
• Starting with the day that you circled, count ahead eight days and draw an X through that day. That's the first day you're likely to be fertile. That's also the first day to practice abstinence or use barrier methods.
• To find the last day you're likely to conceive, subtract 11 days from your longest cycle. If your longest cycle is 30 days, 30 - 11 = 19. Starting from the first circle, count ahead 19 days and draw an X through that date. That's the last day you need to practice abstinence or use barrier methods.

Keep a cycle record for at least eight of your cycles before relying on this method. You must not be using hormonal contraception while you keep these records.

Cost and availability. Using the calendar method costs nothing, but classes that teach this technique may charge fees, which vary from region to region.