Reliability of the rhythm method

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 may be chances for 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.

Advantages of the rythm method 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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