Calendar Method

What Is It?Calendar, Date, Time, Month, Week, Planning, Paper

The Calendar Rhythm Method is a natural form of contraception based on abstaining from sex (or using condoms) during the time that a female is likely to be fertile. The calendar method helps you estimate the time of ovulation (the release of the egg from the ovary) after you have charted the lengths of your menstrual cycles for several months.

How To Use the Calendar Method

  • Keep track of the lengths of your menstrual cycles for 6-12 months. Day 1 is the first day of your menstrual bleeding.
  • After six or twelve months of data collection, find the length of the shortest and longest menstrual cycle.
  • Subtract 18 from the length of your shortest cycle. This tells you the first fertile day in your average cycle. For example, if your shortest cycle was 24 days long, then your first fertile day would be day 6 of your cycle.
  • Subtract 11 from your longest cycle. This will be the last fertile day in your average cycle. For example, if your longest cycle was 32 days long, then your last fertile day would be day 21 of your cycle.
  • During this fertile period (e.g., Day 6 through Day 21) you must abstain from having unprotected intercourse.

When Are You Fertile?

As described above- if your longest cycle was 32 days, and your shortest was 24, you would potentially be fertile from day 6 of your cycle through day 21 of your cycle. The length of potential fertility is greater as the distance between your longest and shortest menstrual cycles increases.

Advantages of the Calendar Method

This method has similar advantages and disadvantages as the other natural methods of contraception.

  • It is completely free
  • It is usable by women with highly variable menstrual cycles
  • Since it is natural, women who oppose “artificial” forms of contraception can use it. In fact, at one point it was the only contraceptive technique supported by the Catholic Church.
  • It does not carry the risk of health effects associated with hormone-based contraception
  • There is no long-term effect on the ability to become pregnant

Disadvantages of the Calendar Method

The disadvantages of this method are similar to the other natural contraception methods, with some additional negative aspects included

  • It has a large window of potential fertility, eliminating the possibility of sex for a large portion of the month
  • Not as reliable as other methods
  • Requires abstinence and/or use of condoms
  • Requires a high degree of attention. The user must be diligent in tracking the length of their menstrual cycles. Corrupt data would lead to corrupt fertility windows.
  • It does not offer protection against sexually transmitted infections.


This method is free to the user.


With perfect use, this method can have a 2% failure rate. However, this is rarely the case. Estimates have placed the annual failure rate at anywhere from 13-24%. This high failure rate, along with its extensive demands on attention and sexuality, make it a rarely recommended and utilized form of birth control.


1. LeVay, Simon, Janice I. Baldwin, and John D. Baldwin. “Contraception and Abortion.” Discovering Human Sexuality. Sunderland, MA: Sinauer Associates, 2009. Print.

2. “Rhythm and Calendar Methods for Birth Control.” Contraception Resource Info. Web.

3. “Calendar-Rhythm Method for Birth Control | Christian Family Planning.” All About Birth Control. Web.

4. Staff, Mayo Clinic. “Rhythm Method for Natural Family Planning.” Mayo Clinic. Web.

Last updated 11 October 2012.