Overview
The rhythm method may be helpful in predicting fertility. It helps people learn when their bodies might be able to get pregnant and when they might not.
The rhythm method also is called the calendar method or the standard days method. It's a type of birth control known as fertility awareness-based contraception. It also may be referred to as a form of natural family planning.
The rhythm method involves tracking menstrual cycles to predict when an egg is released from the ovaries. This process is called ovulation.
If you want to get pregnant, the rhythm method may help you know the best days to have sex to raise the likelihood of getting pregnant. If you don't want to get pregnant, using the rhythm method may help you know which days each month not to have sex or when to use another form of birth control.
Why it's done
For people who want to get pregnant, the rhythm method can help them know the best days to have sex to raise the likelihood of getting pregnant. For people who don't want to get pregnant, using the rhythm method may help them know which days not to have sex or when to use another form of birth control.
Using the rhythm method for either fertility or birth control is low cost, and it doesn't have any side effects. Some people may choose to use the rhythm method as a form of birth control for religious reasons. Others may choose to use it because they cannot use other types of birth control due to medical concerns.
Risks
Using the rhythm method to predict fertility when you're trying to get pregnant doesn't pose any risks.
Using the rhythm method for birth control doesn't pose any direct risks, either. But it doesn't protect you from sexually transmitted infections. And it's less effective than other forms of birth control. Research suggests that about 1 in 4 people using birth control methods based on fertility awareness gets pregnant after a year of typical use.
This approach to birth control requires motivation and commitment. If you don't want to get pregnant, you need to avoid sex or use a barrier form of birth control, such as a condom, during fertile days every month.
How you prepare
Using the rhythm method doesn't require special preparation. But before you begin using it for birth control, it's a good idea to talk with your healthcare professional first. It might not be a good birth control choice if:
- You recently gave birth.
- You recently stopped taking birth control pills or using other hormonal birth control.
- You recently had your first period.
- You're breastfeeding.
- You may be getting close to menopause.
- Your menstrual cycles are not regular.
- You have a medical condition that could interfere with ovulation, such as polycystic ovary syndrome.
What you can expect
There are two forms of the rhythm method: the calendar method and the standard days method.
Calendar method
The calendar method is a more traditional approach. It's not often used anymore because it's easier to make mistakes with the calendar method than with other fertility awareness-based birth control.
The calendar method involves these steps:
- Record the length of 6 to 12 menstrual cycles. Keep track of the number of days in each menstrual cycle. Count from the first day of one period to the first day of the next period.
-
Find the length of the shortest menstrual cycle. Subtract 18 from the total number of days in your shortest cycle. This number is the first fertile day of your cycle.
For example, if your shortest cycle is 26 days long, subtract 18 from 26, which equals 8. In this example, the first day of your cycle is the first day of menstrual bleeding and the eighth day of your cycle is the first fertile day.
-
Find the length of the longest menstrual cycle. Subtract 11 from the total number of days in your longest cycle. This number is the last fertile day of your cycle.
For example, if your longest cycle is 32 days long, subtract 11 from 32, which equals 21. In this example, the first day of your cycle is the first day of menstrual bleeding and the 21st day of your cycle is the last fertile day.
-
Plan sex carefully during fertile days. If you don't want to get pregnant, don't have sex during fertile days. Or have sex using a barrier form of birth control, such as a condom, during fertile days.
If you want to get pregnant, have sex regularly during fertile days.
- Keep tracking your cycles. Continue recording the length of your menstrual cycles every month and update your calculations of fertile days, as needed.
Standard days method
A more modern approach to the rhythm method is the standard days method. It works best for people whose menstrual cycles typically are between 26 and 32 days long.
To use the standard days method:
- Count the days in your menstrual cycle. Start with the first day of your period as day one. Keep counting each day of your cycle until your next period starts.
- Days 1-7 are not fertile days. If you're using the rhythm method for birth control, you can have sex without another form of birth control during this time. You may have menstrual bleeding during these days.
- Days 8-19 are fertile days. If you don't want to get pregnant, don't have sex during these days. Or use another form of birth control during this time. If you're trying to get pregnant, these are the days to have sex.
- Days 20 through the end of your cycle are not fertile days. If you're using the rhythm method for birth control, you can have sex without another form of birth control during this time.
- When you get your next period, start the counting over at day 1.
Keep in mind that many factors, including medicines, stress and illness, can affect the exact timing of ovulation. Using the rhythm method to predict fertility may not be accurate. That's especially true when menstrual cycles aren't regular.
There is a wide variety of apps available to track menstrual cycles that claim to help pinpoint fertile days. But accuracy varies significantly among those apps. The information many of them provide cannot be relied on for birth control. If you're interested in using an app to track fertility, talk with your healthcare professional first about the risks and benefits to decide which app might be a good choice for you.