Calendar Method: Birth Control, Calendars, and Effectiveness

Calendar methods are a type of natural birth control. Although the term ‘calendar method’ is sometimes used to refer to the rhythm method, it actually represents a whole family of contraceptive techniques. Calendar methods rely on the principle of counting cycle days to work out when you’re most fertile. In this article, we’ll take a closer look at how to use these methods and the risks and benefits involved.

Key Takeaways

• Calendar methods are a basic form of fertility awareness that function by counting cycle days to work out the fertile window.
• There are multiple types of calendar methods, including the rhythm method and the Standard Days Method.
• Calendar methods require a six-month monitoring period and are not suitable for those with irregular cycles.

How do I use calendar methods?

Exactly how you use these methods depends on the type of approach you choose. The first step to using calendar methods is to monitor your menstrual cycles and count the days of these for a minimum of six cycles. Your cycle starts on the first day of your period and ends on the last day before your next period, so it’s important to keep track of period dates. By recording when each cycle starts and ends over the six-month timeframe, you can get a good idea of the regularity of your cycles. Once you have this data, you can then do some basic calculations to work out when your fertile days are. On these fertile days, you’ll need to abstain or use barrier protection (such as condoms) to avoid pregnancy.

How to use the rhythm method

Once you’ve recorded at least six months of cycle statistics, you will have an idea of your cycle's average length and regularity. With this information, you can do some basic math to estimate which days are predicted to be safe with respect to avoiding pregnancy. To predict your first fertile day in a cycle:

• Find the shortest cycle out of the ones you have recorded
• Subtract 18 from the total number of days in that cycle
• Count to that number from the first day of your current cycle and mark that day on your calendar (the Xth day of your cycle)
• The day marked X is your first fertile day — you should stop having penetrative vaginal sex on this day (or use a condom) until the last fertile day has passed

To predict the last fertile day in a cycle:

• Find the longest cycle you have recorded
• Subtract 11 from the total number of days in that cycle
• Count to that number from the first day of your period on your current cycle and mark that day with an X
• The day marked X is your last fertile day in the cycle

Keep in mind that if your cycles are usually shorter than 27 days, you should not use the calendar method as birth control.

The Standard Days Method

The Standard Days Method is a simpler example of a calendar method. Instead of calculating based on your own cycle dates, the Standard Days Method simply allocates cycle days 8 to 19 as fertile days for everyone. Users should abstain from sex or use protection during this window.

Summary of Calendar Calculation Methods