You may have heard of the ‘rhythm method’ in regards to birth control, but it can be used to promote fertility as well. In fact, as birth control, it’s highly ineffective for preventing pregnancy, but when the principles are reversed—to determine your fertile window, or peak fertility days—it can be very helpful.

When couples or people with uteruses are struggling with getting pregnant and come to visit us at Arizona Center for Reproductive Endocrinology & Infertility, we always ask them about their menstrual cycles and history. With the rhythm method—regardless of how you plan to use it—it’s extremely important to keep close tabs on your cycle, and therefore can help you relay crucial information to our team.

Here’s what you should know.

What is the Rhythm Method?

The rhythm method, which is also sometimes called the calendar method or the calendar rhythm method, is a form of natural family planning. It can be used as a way to promote fertility or as a method of contraception, by helping you determine the best days to have or avoid unprotected sex. When you’re trying to get pregnant, you can use the rhythm method to determine when you’re at your peak fertility, and should be having intercourse.

(In contrast, you could also use the rhythm method to avoid pregnancy, using it to determine which days you’re most fertile and avoid having unprotected sex on those days. Some women choose to use the rhythm method if a medical reason limits their traditional birth control options, or for religious reasons. It’s important to note, however, that several factors, including medications, stress, illness, and underlying medical issues, can affect the exact timing of ovulation. This is why using the rhythm method as a form of natural birth control can be ineffective, especially if your cycle is irregular.)

How It Works

Using the rhythm method to achieve a pregnancy requires careful record keeping and persistence. For the most accuracy, you must keep detailed track of your menstrual history in order to predict when you’ll ovulate. Again, this helps you determine when you’re most fertile and most likely to conceive. This is how you’d do it:

1. Record the length of six to 12 of your menstrual cycles. Use a calendar or notebook to write down the number of days in each menstrual cycle, beginning from the first day of one period to the first day of the next period. There are also several period tracking and fertility tracking apps that can help you record these dates.
2. Based on what you’ve tracked, determine the length of your shortest menstrual cycle. Then subtract 18 from the total number of days in your shortest cycle. This number represents the first fertile day of your cycle. For example, if your shortest cycle is 24 days, subtract 18 from 24; your answer is six. In this example, the first day of your cycle is the first day of your period, and the sixth day of your cycle is the first day of your fertile window.
3. Now, determine the length of your longest menstrual cycle. Subtract 11 from the total number of days in your longest cycle. This number represents the last fertile day of your cycle. For example, if your longest cycle is 35 days, subtract 11 from 35; your answer would be 24. Again, in this example, the first day of your cycle is the first day of your period, but the 24th day is the last day of your fertile window.
4. Plan for intercourse during your fertile days.

For the most accuracy using the rhythm method, it’s important to update your calculations every month, since the length of your cycle—which affects your fertile window—can change.

Relying solely on the rhythm method to achieve a pregnancy doesn’t work for everyone—especially if your cycles are irregular or if you’ve tried to conceive for several months with no success.

At AZCREI, we want to help you realize your dreams of having a happy, healthy baby, and we have several options to help you do so. If you’d like to discuss the rhythm method as a fertility or birth control method or to get started on your fertility journey, schedule an appointment with our team by calling (520) 326-0001 or visiting us online.