How Effective Is Your Birth Control Pill, Really?

Photographed by Jessica Nash.
By Kendall McKenzie
“Why are there sometimes two different effectiveness rates for birth control? Which is correct?”
One of the questions we get all the time is, “How effective is birth control?” Usually, people are looking for one, definitive percentage that tells them exactly how well a certain method prevents pregnancy. But, reality is more complicated than that.
Birth control effectiveness is measured two ways: how well it prevents pregnancy when used PERFECTLY every single time, and how well it prevents pregnancy after factoring in human error. These are called “perfect-use rates” and “typical-use rates.”
Let’s look at the birth control pill, for example:
Perfect-use rate: Less than one out of 100 people will get pregnant each year if they ALWAYS take the pill every day as directed.
Typical-use rate: About nine out of 100 people will get pregnant each year if they don’t always take the pill each day as directed.
So, the pill is extremely effective if used perfectly, but that old saying, “nobody’s perfect,” also applies to birth control. We sometimes make mistakes, or life circumstances foil our perfect-use plans: things like forgetting a pill, losing a pill, not being able to get the next pack on time, and barfing can all impact the pill’s effectiveness. Therefore, we have two different rates, and the “real-life” one applies to most of us.
But, what’s up with birth control that has only one, very impressive effectiveness rate? (Lookin’ at you, IUDs and implants!) These LARCs — long-acting reversible contraceptives — are virtually impossible to screw up. So, they get a perfect-use rate by default: more than 99% — the best there is. More and more people are using LARCs these days because they’re super convenient AND super effective — even the folks on our Planned Parenthood Tumblr Team are huge fans.
Stuff happens, so typical-use rates are the most true-to-life. The most common reason birth control fails is because we mess it up. So, whatever method you choose, you’ve got to use it as perfectly as possible, or it just won’t work as well as it should. Be honest with yourself: If your lifestyle doesn’t jive with having to think about birth control on a regular basis, consider getting yourself a LARC.
And, remember: No method of birth control is 100% effective, even if used perfectly. But, you can increase your pregnancy-preventing superpowers by using both birth control and condoms. Here’s another really good reason to do that: Condoms are the only method of contraception that also protects you from STDs.

More from Sex & Relationships


R29 Original Series