What Is the Rhythm Method of Birth Control?

The rhythm method of birth control, also known as natural family planning or fertility awareness, is the process of tracking your monthly menstrual cycle to help you either avoid pregnancy or become pregnant.

Women are fertile for only a few days each month. If you want to become pregnant, the rhythm method can help you identify the days when you are most likely to become pregnant (before ovulation) or, if you want to avoid pregnancy, when you should not have sex.

This article will discuss how to use the rhythm method as a form of birth control.

Young cheerful spouses enjoying morning time together

YakobchukOlena / Getty Images

The Menstrual Cycle

A woman's body goes through a menstrual cycle, which is a series of naturally recurring processes, each month during her childbearing years.

When you are not pregnant, hormones (chemical substances that your body produces) cause you to menstruate, which is the shedding of the lining of your uterus. Most months, your body will produce another egg, and if the egg is not fertilized, the cycle starts again.

How to Track Fertility

The rhythm method depends on close tracking of the days you are most likely to be ovulating. After your period, the level of the hormone estrogen begins to rise, causing small sacs, known as follicles, in your ovaries to produce another egg. When you ovulate, the egg moves into the fallopian tubes, where sperm can fertilize it, resulting in a pregnancy.

Most women will ovulate somewhere between day 11 and day 21 of their cycle. Ovulation may not happen on the same day each month, though, and if you are sick or stressed, for example, your health may affect your cycle.

There are several ways to count the days in your menstrual cycle to identify when you are most likely to be fertile.

Effectiveness of the Rhythm Method

Due to the efforts needed to correctly track ovulation, the rhythm method is not as effective as other forms of birth control. However, if you have health concerns that prevent you from using other, mostly hormone-based birth control methods—or you have religious or other reasons for choosing natural birth control—the rhythm method is an alternative. Discuss your birth control options and the rhythm method with your healthcare provider.

Traditional Calendar Rhythm Method

The traditional calendar method of birth control relies on you to track data from your previous menstrual cycles to predict your fertile days.

The traditional calendar rhythm method includes the following steps:

  • Track your menstrual cycle on a calendar for at least six months before using the rhythm method.
  • Each month, mark the first day of your period, then count the number of days until the first day of your next period. The days between your periods may vary. For instance, one month it might be 28 days and the next month it might be 27 days.
  • Find your first fertile day by finding the shortest number of days between periods and subtract 18. For example, if your shortest day was 28 days, subtract 18 to get 10.
  • Use that number to count the days from the first day of your period. That is likely your first fertile day.
  • Find the last fertile day by finding the longest cycle you tracked and subtract 11. Say your longest cycle was 30 days, so subtract 11 to get 19.
  • Use that number to count the days from the first day of your period. This is likely your last fertile day.

The calendar method gives you a rough idea of when you may be fertile, but it is not precise or 100% effective.

Standard Days Method

If your menstrual cycle is very regular and between 26 and 32 days long, you can try the standard days method of family planning.

It includes the following steps:

  • Use a calendar or app to count the days from the first day of your period. Do not have vaginal intercourse between day 8 and day 19 of your menstrual cycle.
  • If you do have sex during this period, use some other form of birth control if you do not want to become pregnant.
  • You can use beads on a string, called CycleBeads, as a visual tool to help you track your cycle. There are also various apps that can help you track days.

Factors that Affect Standard Days

If you have recently been pregnant, are breastfeeding, or have taken birth control pills, cycle tracking methods will be less reliable. Consult your healthcare provider before you begin using natural family planning.

Other Signs of Ovulation

The rhythm method is not as effective as other forms of family planning. If you choose to use it, you can also watch for changes in your body that can help you identify when you are fertile.

Changes in Cervical Mucus

Cervical fluid will become thicker, like the consistency of an egg white, when you are close to ovulation. After ovulation, you will have less mucus discharge.

Changes in Cervical Texture and Position

When you are fertile, your cervix moves higher in your body. You may find it hard to reach with your fingers compared to other times in your cycle. Your cervix will feel softer, moister, and more open, which are changes that make it easier for fertilization to occur.

Body Temperature

When you ovulate, your body temperature rises slightly, less than 0.5 degrees. You can use a basal body temperature thermometer to track this increase, which is very precise and shows temperature changes to one-tenth (0.1) of a degree.

Check your temperature carefully at the same time each day when you are at rest. Over time, you will begin to see a pattern and predict when you are likely to be ovulating.

Ovulation Test Strips

Ovulation test strips, which you can buy in over-the-counter kits, can tell you when you are approaching ovulation. They measure the amount of a substance called luteinizing hormone, or LH, in your urine.

If a surge is detected, you will likely ovulate in the next 24–36 hours, so begin using the strips two days before you think you will ovulate, carefully following the instructions in the kit.

Risks of the Rhythm Method

There are some risks with the rhythm method of birth control, a primary one being that it does not protect you against sexually transmitted diseases (STDs). It also takes months of tracking to establish a pattern before you can use it accurately. Generally speaking, natural family planning methods, including the rhythm method, are only effective 76%–88% of the time.


The rhythm method of family planning is a natural way to prevent or promote pregnancy. It requires careful attention to your menstrual cycle and logging the days of your period, as well as calculating when you are most likely to be fertile. You can supplement it by noting changes in your body or using ovulation predictors, such as test strips, but it is not as effective as other means of birth control if you want to avoid pregnancy.

A Word From Verywell

Deciding to become pregnant and avoiding a pregnancy are significant issues women face throughout their lives. If you are considering the rhythm method of birth control, consult with your healthcare provider to make sure you have all the facts and that you are administering it properly.

Frequently Asked Questions

  • How effective is the rhythm method?

    Experts have estimated the effectiveness of the rhythm method is anywhere between 76% and 88% effective with typical use, which requires persistence and attention. It is considered one of the least effective methods of birth control, but combining it with other methods, like observing changes in the cervix and using ovulation test strips, can increase the effectiveness.

  • What other birth control options are currently available?

    In addition to natural family planning, including the rhythm method, women today have various birth control options. These include IUDs (intrauterine devices) or implants, hormonal birth control (by pill, injection, or inserted ring), and barrier methods (including condoms, diaphragms, and cervical caps). Other forms like spermicide, contraceptive gels, and sponges are less effective.

  • What if I had sex when I might have been ovulating?

    If you do not want to be pregnant and are concerned that you might be pregnant because you had unprotected sex when you were ovulating, you can use a morning-after pill, like Plan B, which is considered emergency contraception. Emergency contraception is not 100% effective, but it can significantly reduce your risk of pregnancy if you use it within 72 hours of unprotected sex. You can buy a morning-after pill over the counter in drugstores.

8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Planned Parenthood. Fertility awareness.

  2. Planned Parenthood. What's the calendar method of FAMs?

  3. Weis J, Festin M. Implementation and scale-up of the standard days method of family planning: a landscape analysisGlob Health Sci Pract. 8(1):114-124. doi:10.9745/GHSP-D-19-00287

  4. Planned Parenthood. What's the standard days method?

  5. Planned Parenthood. What's the cervical mucus method of FAMs?

  6. Cleveland Clinic. Basal body temperature.

  7. U.S. National Library of Medicine. Ovulation home test.

  8. Plan B One-Step. What is plan B?

By Nancy LeBrun
In addition to her extensive health and wellness writing, Nancy has written about many general interest topics for publications as diverse as Newsweek, Teen Vogue, abcnews.com, and Craftsmanship Quarterly. She has authored a book about documentary filmmaking, a screenplay about a lost civil rights hero, and ghostwritten several memoirs.