The Calendar Method of Family Planning: A Step-by-Step Guide

There are a few natural family planning methods that can help inform a woman of her most fertile days, like the Billings ovulation method and basal body temperature method. The calendar method (also called the rhythm method) may be the most commonly known. All of them, however, rely on a woman observing changes in her body, like her menstrual cycle. 

Similar to all natural family planning methods, for the calendar method to be effective, instructions should be followed correctly. More importantly, data tracking and computations should be consistent and accurate. 

Be prepared, it will take quite a bit of work. But, if you think that this method is right for you and you are fully committed to it, it can be an effective method to plan your family.  Read through the following carefully.

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How to use calendar method

Step 1

A. Before you can use the calendar method, you need to track your period. For 6 to 12 months, write down the first day of your period.

B. Count the number of days between each cycle – or between each first day of your period. 

• For example, your first day landed on October 5. After, your next first day landed on October 31. The days between these is 26. Track your first days for at least 6 cycles.

Note: If you notice that your cycles are shorter than 27 days or that you are very irregular, the calendar method will not work for you. 

Step 2

A. Find your shortest cycle in the dates that you recorded. 

• For example, from January to August, your shortest cycle (or days between the “first days”) was 26 days.

B. Subtract 18 from this shortest cycle

• 26 days minus 18 equals 8.

C. Now, from the first day of your period, count forward to the number you got in Step 2 B. This is the start of when you are fertile. Sexual contact on this day, and the days until your last fertile day, may result in pregnancy.

• If the first day of your period is October 5, you count forward 8 days (including the first day). The date you will get is October 12. This is the first day that you are fertile. 

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Step 3

A. Find your longest cycle in the dates that you recorded.

• For example, from January to August, your longest cycle was 32 days.

B. Subtract 11 from this longest cycle

• 32 days minus 11 equals 21.

C. Now, from the first day of your period, count forward to the number you got in Step 3 B. This is the last day of when you are fertile.

• If the first day of your period is October 5, you count forward 21 days (including the first day). The date you will get is October 25. This is the last day that you are fertile.

Step 4

The days you are most likely to get pregnant when you have sex are the days on and between Step 2 C and Step 3 C.

• Your fertile days are on October 12 to 25. Have intercourse on these days if you are trying to conceive and avoid them if not. 

Continue tracking your mentrual cycle and counting the days in between the “first days.” This way you'll know if the “shortest” or “longest” have changed. Take note as well that, according to Cosmo.ph, the calendar method's effectiveness is low (80% at most) due to a high possibility of miscalculation. For other family planning methods available, both natural and artificial, click here.

Sources: Planned Parenthood, Mayo Clinic

This article was updated on March 19, 2019 at 7:39 p.m.

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