Rhythm Method

Not all women are comfortable with using birth control methods that involve hormones, like the birth control pill, or like the feel of using barrier contraceptives, such as the sponge. Whether for personal or religious reasons, numerous women opt for natural family planning (NFP) as their contraceptive of choice. Though not the most reliable or effective birth control around, the rhythm method is one that has long been used by women all over the world.


Rhythm Method

This method is also known as fertility awareness, periodic abstinence or the calendar method. It is a way of avoiding pregnancy by simply not having intercourse during the days when you ovulate. Many couples wishing to have a child also use this method to time intercourse during the time of ovulation in order to improve their chances of conception.

If you wish to use this method of birth control, you will need to track your menstrual cycle to understand your body’s pattern and know precisely the days when you are most fertile. Then, by avoiding intercourse on those days or using other birth control options, such as condoms, it may be possible to prevent pregnancy.


How Does it Work?

This method of natural birth control is based on an individual’s menstrual cycle. Typically, sperm can survive inside the female reproductive system for around 5 to 7 days, but an egg can only live for 24 hours. Therefore, it is possible that your egg may get fertilised even 2 or 3 days after intercourse when ovulation occurs and sperm is already present in the body. However, 24 hours after you have ovulated, it is fairly safe to say that pregnancy will not occur until your next menstrual cycle. But how can you know just when you are most fertile?

Most menstrual cycles can be divided into three phases:


  • Pre-ovulatory infertility phase
  • Fertility phase
  • Post-ovulatory infertility phase


The first day of your period is considered to be the first day of your cycle. In order to determine the pre-ovulatory infertility phase, you will need to track your menstrual cycles for at least six months. After this time, take your shortest cycle and subtract 19. For example, if your shortest cycle was 26 days, then you would subtract 19 from 26. This would leave you with 7; you will remain infertile until the 7th day of your cycle.

The post-ovulatory infertility phase is calculated by deducting 10 from your longest menstrual cycle. For example, if your longest cycle was 32 days, then 10 from 32 would be 22. Therefore, on the 22nd day of your cycle you would resume another infertile period. This would also mean that, from day 8 to 21 of any given cycle, it would be necessary for you to abstain from sex or use another contraceptive method, as the likelihood of pregnancy is significantly increased at this time.


Who Can Use It?

Most natural birth control methods need you to be very aware of each and every change that occurs in your body. Knowing the length of your monthly cycles, noticing the changes in your cervical mucus and paying attention to changes in your body temperature can all help to keep you aware of your fertility. Therefore, those who have irregular cycles cannot really benefit from the Calendar Rhythm Method. Additionally, teenagers, who often do not have regular cycles yet, are also advised against using this method.

Because this method requires the use of periodic abstinence, it is recommended more often for people in long-term relationships. Furthermore, the rhythm method offers no protection against STDs, like HIV and chlamydia. This is another reason why it is more often recommended for couples in long-term, monogamous relationships where both partners have tested free of STDs.

It is always better to consult your physician before practising this method, as he will be able to advise on the exact way you can track your cycle and if you need to use any other devices that might help in knowing your ovulatory phase.



Imperfect use of this birth control option or having intercourse during the fertile days has lead to a relative increase in the failure rate of rhythm method. Of about 100 women using this method, around 25 may get an accidental pregnancy. Even with perfect use, though, the rhythm method is still only 91% effective meaning, out of 100 women who use this method perfectly, nine will be become pregnant every year.



There are many factors that make rhythm method a not very reliable way of birth control. Apart from the usual mistakes that anyone can make, like tracking your cycle incorrectly, using the wrong formula to find the infertile or fertile phase, having intercourse during fertile days or maybe unwillingness of a partner, this method also has certain flaws.

The formula used to determine your fertile time is based on the assumption that all women ovulate halfway through their menstrual cycle. Although many women do ovulate halfway through, others ovulate earlier on while some don’t ovulate until just before their period. Also some women get mid-cycle bleeding that they may mark as a normal menstrual cycle, leading to a wrong calculation of cycle days. As a result, your fertile phase may not be accurately predicted, causing you to unknowingly have intercourse during a fertile time.

Another reason for the increased failure rate is that you use past cycles to predict future cycles. In most cases, past patterns are sufficient in providing you with a guideline for future cycles. However, any changes to your lifestyle, such as taking medication, dealing with stress, illness, starting menopause or breastfeeding, and chances are that your cycle may change. Even without these factors, the reality is that all women have a slightly different cycle every month. And this can affect just when you ovulate and are fertile during a cycle.

With numerous other methods of birth control available nowadays, the rhythm method is used more often as an added safety measure and a way of knowing your body better rather than as a primary form of birth control.



As a natural birth control method, using the rhythm method to track your fertile days is relatively simple compared to using a contraceptive patch or receiving hormone injections. Other advantages are:


  • Almost anyone can practice it
  • Does not require any apparatus
  • Does not interfere with foreplay or intercourse
  • Has no effect on long-term fertility




One of the biggest disadvantages of the rhythm method is that it does not protect against STDs. Other disadvantages include:


  • Takes a lot of time to track the monthly cycle
  • You cannot start using this method instantly and will need to note your cycles for at least 6 months first
  • Partner may not be willing to cooperate



Side Effects and Cost

Unlike other birth control, the rhythm method does not have any birth control side effects associated with its use. Additionally, costs for this contraceptive are minimal as all you really need is a calendar and a pen. However, before starting this method of contraception, it is best to discuss all its pros and cons with your health care provider.

Join our Birth Control forum to find out what other women are saying about the many various methods of contraception.

For more information on natural birth control, visit our Timing Intercourse page.

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