An explanation of contraceptive failure rates

Dear Alice,

When people say that contraceptives, like condoms, have a twelve percent failure rate, do they mean that they result in pregnancy in twelve out of every 100 women who use them? I hope that means that twelve percent of people who use them become pregnant in a year, or something like that. Otherwise, it sounds as risky as Russian roulette to rely on condoms.

Dear Reader,

You’ve got it, partly — the effectiveness of contraceptive methods are measured by its pregnancy prevention rate, but condoms aren't a risky gamble by any means. The effectiveness of contraceptives depends heavily on how consistently and correctly people use them. During a year of typical external (male) condom use, about 13 out of 100 sexually active people become pregnant. On the flip-side, during a year of perfect condom use, that number drops to about 2 out of 100. As for the internal (female) condoms, about 21 percent (typical use) and 5 percent (perfect use) of people who use this type of condom experience an unintended pregnancy within the first year of use. So, the more consistently and correctly condoms are used, the more effective they are — that’s why it’s helpful to practice using them. Each type of contraceptive has its own rate for perfect use and typical use. Knowing this information, as well as what makes that contraceptive more or less effective, can help determine what the most appropriate form is for that person and their partner(s).

It might also be helpful to talk about the difference between perfect use and typical use of contraceptives. Perfect use is defined as using the contraceptive during sex consistently and correctly every single time and reflects the effectiveness of the contraceptive itself. For example, perfect use of condoms means using them correctly every single time during sex. Typical use, on the other hand, gets at the reality that people may use contraceptives incorrectly or may not use them every single time they have sex. That is, the typical use effectiveness rates include the possibility of human error (such as using a condom that's the incorrect size, using an expired condom, or improperly securing the internal ring with an internal condom) or omission among those who report using condoms. For example, a self-reported condom user could take a condom off too early while having sex. It follows that typical use contraceptive effectiveness is lower than perfect use — if someone uses a condom nine out of ten times they have sex, then there’s a higher chance of pregnancy than if they use a condom 100 percent of the time.

On the subject of effectiveness, it’s also helpful to note that condoms are also highly effective in preventing transmission of HIV and a number of other sexually transmitted infections (STIs). The Centers for Disease Control and Prevention (CDC) estimates that external condom use reduces the chance of getting HIV by 63 percent to 80 percent, depending on the person's sex assigned at birth and their type of sexual activity. Condoms also reduce the risk of other STIs, but their exact effectiveness also depends on several different factors, including demographic and behavioral factors. 

You and your partner(s) can also use other methods of birth control in conjunction with condoms, as well as have emergency contraception on hand so that it can be taken as soon as possible in the case that it's needed. This can help decrease the risk of pregnancy and can address the human error that may occur with condom use. To make the best use of condoms, practice using them! You or your partner(s) may also want to try using condoms during (mutual or solo) masturbation — there may be less pressure and anxiety than during sex, so it might be easier to get the hang of the steps.

Hope this helps,

Last updated Nov 05, 2021
Originally published Aug 30, 2002

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