When evaluating a contraceptive method, the first question you will likely ask is "How effective is it?" It is a critical question, because after all, if you are sexually active and wish to prevent pregnancy, you need a reliable birth control method.  

But you may be surprised to know that when different methods are described as "highly effective," "moderately effective" or just plain "effective," this only gives you part of the story. There are other factors to take into consideration that will determine how successful a method is for you. 

In two past blog articles, we described in detail how effectiveness is measured. Efficacy rates indicate how effectively women avoid pregnancy in the first year of use. These rates are measured both for "Perfect Use" and "Typical Use".


  • Perfect Use is when you use a method correctly and consistently all of the time.
  • Typical Use is how an average person actually uses a method in real life. This can be a little less clear. We all like to think that we would use our chosen family planning option correctly, but what happens if you forgot to take your pill one morning or if you jumped out of bed before taking your temperature?


Both Perfect Use and Typical Use effectiveness need to be examined when making a decision on which method to choose. It is also important to know that the longer you use a method, the better you become at using it.  With all contraceptive methods, unintended pregnancies are most likely to occur in the first three months of using the method. This is true with the research on the Standard Days Method® and CycleBeads®, where almost all of the pregnancies that occurred during testing occurred within the first 3 months.  And it is similar with all contraceptive methods.

So if you have used a method three months or longer without an unintended pregnancy, you could expect that Typical Use efficacy for you would be higher than the quoted rate. This is an important point. The failure rate of a method is not additive over time as has been incorrectly shown in a recent misleading graphic in the New York Times.  But while we know that the Typical Use failure rate is likely to improve over time, there are very limited studies on long-term effectiveness beyond the first year of use. 

Any modern method of birth control can be effective -- and effective over time. Individual factors such as lifestyle, motivation, commitment to correct use, and even partner cooperation can affect the success of your chosen method. When choosing a method, it is important to keep in mind that you will be most successful with a method that:


  • you want to use and will fit your needs and stage of life
  • you can use correctly and consistently
  • you can deal with its potential side effects
  • you can use with existing medical conditions
  • you can access easily


Related Blog Posts:

What Does "Effective Family Planning" Really Mean?

Birth Control Effectiveness: How Risky is Your Birth Control?

Posted in: Birth Control Effectiveness, Birth Control Options, Contraceptive Options

Tags: birth control, contraception, birth control efficacy, Perfect Use, Typical Use Contraceptive Choice, women's reproductive health, birth control options for women

4 comments for "Birth Control Effectiveness: What Determines Success?"

Jenna says:

Yes! Great points. We'd all be pregnant 10x over if the info in the nyt graphic was true. Thanks for explaining this do clearly.

Camille Guerrier says:

Thank you for sharing this article. We should all take into consideration the importance of family planning. Like you said, the concept of family planning is preparing ourselves to be a responsible parent. We should consider the amount of children that we would be able to support and take care of well. As you said, family planning can even help mothers pursue careers or other activities. Thanks again. -Camille | http://www.obgynmedicalgroup.com/Obstetrics-Services-Infertility-Treatments-Whittier-CA.html

Dr. Stewart says:

You have absolutely no idea what you're talking about. The calculated expected effectiveness over 10 years isn't the running rate of failure; it's the cumulative probability of an occurrence of failure over that length of time.

But hey, just because you don't understand something, don't let that stop you from playing the expert on the Internet!

Pop quiz: If you pick a day of a year at random, there is a 1/365.25 probability that the day you picked is July 1st. If you do that for 10 consecutive years, there is still a 1/365.25 probability that any given pick is July 1st. But, and here's where you get lost, what is the probability that, of your 10 picks, at least one is July 1st? I'll give you a hint, it's not 1/365.25.

Ann Mullen says:

In response to Dr. Stewart's comments, the NYT graphic is a flawed way of expressing contraceptive failure over time, because contraceptive failure is not a fixed risk. It's not flipping coins or picking random dates. Probability of pregnancy is reduced over time, because typical use improves with experience; and women who are not well suited for a method would get pregnant and/or drop out sooner. Women who use a method without a pregnancy over a certain time are more likely to continue using the method without a pregnancy.

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