How Do You Interpret Birth Control Failure Rates?

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Confused about how effective different forms of birth control are? For example, if you read that the failure rate of condoms is 2-15% when 100 couples have sex regularly for a year, you might wonder what that actually means.

In order to choose the best birth control method for you and to maximize its effectiveness, it is important that you understand how to interpret birth control failure rates.

What is a Birth Control Failure Rate?

The birth control failure rate is the frequency with which a particular birth control rate fails (for this purpose, failure means that pregnancy is not prevented by the method, aka a pregnancy occurs). Failure rates are meant to be fairly reliable estimations of birth control effectiveness. Most failure rates are determined in clinical research studies with sample populations of participants.

Theoretically, it is possible that different subject pools using the same birth control method can generate different failure rates. Researchers try to minimize this by using a large number of diverse participants. Failure rates, in research, can also be affected by demographics, educational levels, culture, and the instruction technique that is used to teach how to use the contraceptive method.

How is a Birth Control Failure Rate Calculated?

Failure rates are typically calculated for each birth control method based on the number of pregnancies that are avoided by using that contraceptive. This an also be expressed as the difference between the number of pregnancies expected to occur if no method is used, and the number expected to take place with that method.

So, what does it mean when you read condoms have a 2-15% failure rate? Well, another way to understand this is that condoms are 85-98% effective. The effectiveness rate is the opposite of the failure rate. Subtract the failure rate from 100, and that number is the birth control effectiveness rate. Condoms are 85-98% effective (meaning they have a failure rate of 2-15%).

This means that for every 100 women whose partners use condoms, 2 to 15 will become pregnant within the first year of use. So basically, the failure rate does not refer to how many times you have sex, it correlates the number of people (100) who use that method over the course of one year.

Typical Use vs. Perfect Use

The reason why you may see a range in the rates has to do with "typical use" vs. "perfect use:"

  • Typical use failure rates tend to represent how the average individual uses contraception. These rates apply to folks who became pregnant while not always using their contraception correctly and/or consistently. In reality, many people find it challenging to always and reliably use contraception correctly.
  • Perfect use failure rates reflect pregnancies that occurred with individuals even though they always used their contraception correctly and consistently.

Typical user failure rates tend to be higher than perfect use because in this scenario, the contraceptive is not being used perfectly. So, when the failure rates are presented in a range, the lower number represents perfect use and the higher number is for typical use.

Birth control methods that require more for a person to do (i.e., remember to use, be inserted or put on a certain way, be used within a certain timeframe, etc.), tend to have higher failure rates because there is more room for error.

These methods include:

Sometimes, you will not see a range in failure rates. This means that typical use is equal to perfect use. This tends to be the case for contraception that is inserted or performed by a doctor. Once this happens, there is virtually nothing for a person to do, so this eliminates typical user errors. Examples of contraceptives with equal perfect use and typical use failure rates are:

One last thing to keep in mind when it comes to birth control failure rates is that they usually refer to the number of people (out of 100) who use that birth control method and who will become pregnant during the first year of use.

In practice, it appears that the failure rates tend to be higher during the first year that you consistently use one particular contraceptive. There are several reasons why failure rates may decrease after using a method for one year. These include:

  • The more experience you have using a birth control method, the more effective it becomes. The longer you use a method, the more comfortable and better skilled you become at using it. This should help to reduce typical user errors.
  • Less motivated users may become pregnant and stop using contraception (leaving those who are still using a particular method after a year to be more serious and devoted users).
  • A woman’s fertility level decreases with age, so with each year that passes, she is less likely to become pregnant.

Making a Decision Based on Failure Rates

When comparing birth control methods, pay attention to whether the posted numbers refer to failure rates or effectiveness rates, as well as typical use or perfect use. Keep in mind that, regardless of the posted effectiveness or failure rate, other factors (in addition to user error or inconsistent use) can lower the effectiveness of birth control methods. These can range from your motivation to your weight to certain medications that you use.

The frequency that you have sex may also be one of your criteria for choosing a birth control method. Basically, if you know that you will be having sex very frequently, it may be a wiser choice to use a more effective method to have the best chances of not getting pregnant.

Understanding how to interpret failure rates, knowing factors that could influence contraceptive’s effectiveness, evaluating your lifestyle and sexual behavior, and determining the level of effectiveness that is most acceptable to you can greatly help in any birth control decision that you make. Consult with your doctor or midwife for help in making a decision about what method will work for you and your lifestyle.

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Article Sources

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial policy to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  • Centers for Disease Control and Prevention. Contraception. 2019.

  • Trussell J. Contraceptive failure in the United States. Contraception. 2011;83(5):397–404. doi:10.1016/j.contraception.2011.01.021