Calendar/Rhythm

What Is It?

Charting menstrual cycle to help detect fertile days. Abstinence from sex during fertile days ("unsafe days").

How Does It Work?

Users abstain from sex on fertile days to prevent egg and sperm from meeting. Fertilization does not occur.

How Is It Used?

Woman charts menstrual cycle on a calendar. Fertile days are calculated based on the following assumptions: 1) ovulation occurs on day 14 (plus or minus 2 days) before the onset of the next menstrual period; 2) sperm live for 2-3 days; and 3) the egg lives for 24 hours.

How Well Does It Work?

Typical use: 75%. Perfect use: 91%.

What Are Its Main Advantages?

No health risks or side effects caused by method. Accepted by most religions. Can also be used to determine fertile days when pregnancy is desired. Responsibility can be shared by couple.

What Are Some Possible Problems?

Menstrual cycle can change due to stress, illness, or other factors making it difficult to predict ovulation and fertile days based on past cycles. Have to abstain from intercourse on fertile days (back-up method can be used on fertile days, if couple chooses not to abstain). Temptation to take risks may occur. Care is needed to keep records.