The chances of birth control not working depend entirely on which method you use and how consistently you use it. The most common method, the pill, fails about 9% of the time in real-world use, meaning roughly 9 out of 100 women using it will get pregnant within a year. Long-acting methods like IUDs and implants bring that number below 1%.
The gap between how well a method works in theory and how well it works in everyday life is the most important thing to understand about contraceptive failure.
Typical Use vs. Perfect Use
Every contraceptive has two failure rates. “Perfect use” is what happens in clinical conditions when someone follows every instruction flawlessly. “Typical use” is what actually happens in real life, where people forget pills, store medications incorrectly, or don’t follow timing rules exactly. For most people, typical use is the number that matters.
Here’s how common methods compare, based on the percentage of women who experience an unintended pregnancy during the first year:
- The pill, patch, or ring: 9% typical use, 0.3% perfect use
- Male condoms: about 13% typical use, 2% perfect use
- Copper IUD: 0.8% typical use, 0.6% perfect use
- Hormonal IUD: 0.2% typical use, 0.2% perfect use
- Implant: 0.05% typical use, 0.05% perfect use
Notice the pattern: the methods you don’t have to think about every day (IUDs and the implant) have nearly identical typical and perfect use rates. The methods that require daily or per-encounter action have enormous gaps, because human error enters the picture.
Why the Pill Fails So Often
That 9% failure rate for the pill isn’t because the medication itself is unreliable. When taken at the same time every day without missing a dose, the pill prevents pregnancy 99.7% of the time. The problem is that very few people manage that consistently for an entire year.
For combined pills (the most commonly prescribed type), a pill is considered “late” if fewer than 24 hours have passed since you should have taken it, and “missed” once you hit the 24-to-48-hour window. Missing two or more pills in a row, meaning 48 or more hours since your last dose, significantly raises your pregnancy risk and typically requires backup contraception. The more pills you miss in a cycle, and the closer those missed pills fall to your pill-free week, the higher the chance of ovulation breaking through.
How Condoms Fail
Condoms have a relatively high typical-use failure rate, but outright breakage and slippage are less common than most people assume. In studies tracking condom performance, about 2% of condoms broke during intercourse and 1% slipped off. That means the majority of condom “failures” come from inconsistent use: not putting one on from the start, removing it too early, or not using one at all during some encounters. Using oil-based lubricants with latex condoms also weakens the material and increases breakage risk.
Why IUDs and Implants Rarely Fail
Long-acting reversible contraceptives work so well because they remove human error from the equation. Once an implant is placed in your arm or an IUD is inserted, there’s nothing to remember, no timing to get right, and no prescription to refill. The implant has a failure rate of just 0.05%, making it the most effective reversible contraceptive available. The hormonal IUD sits at 0.2%. The copper IUD, while slightly less effective at 0.8% in the first year, remains highly effective over its full 10-year lifespan, with a cumulative failure rate of about 1.9% over a decade, comparable to surgical sterilization.
The main way these methods can fail is if the device moves out of position. IUD expulsion happens at a rate of roughly 15 per 1,000 users per year. Your risk is higher if you have heavy periods, are 24 or younger, or have had four or more pregnancies. Signs of expulsion include feeling the hard plastic of the IUD at your cervix, unusual cramping, or noticing that the strings feel longer or shorter than before. If the IUD shifts without you realizing it, you lose protection without knowing.
Medications That Reduce Effectiveness
Certain prescription drugs can lower hormone levels from the pill, patch, or ring enough to allow ovulation. The biggest culprits fall into a few categories.
Some seizure medications are the most common offenders. Drugs prescribed for epilepsy, bipolar disorder, and nerve pain can speed up how quickly your liver breaks down contraceptive hormones. If you take medication for any of these conditions, your provider should discuss whether your birth control needs to be adjusted.
One specific HIV medication, efavirenz, has been shown to significantly reduce hormonal contraceptive effectiveness. Other antiretrovirals have raised some concern in studies but haven’t shown the same clear impact.
Among antibiotics, rifampin (used for tuberculosis) is the only one proven to interfere with hormonal birth control. Despite a widespread belief that all antibiotics reduce pill effectiveness, this isn’t supported by evidence for commonly prescribed antibiotics like amoxicillin or azithromycin. Rifampin is rarely prescribed in general practice, so this interaction affects very few people.
These drug interactions don’t affect IUDs or implants in the same way, since those methods deliver hormones locally or work through non-hormonal mechanisms.
Heat, Storage, and Damaged Medication
Hormonal birth control contains proteins that can change structure when exposed to excessive heat. Most medications are labeled for storage between 68 and 77°F, with a tolerable range up to about 86°F. Above that, the active ingredients may start to degrade. A car’s interior can climb to roughly 50% above the outside temperature within a short time, which means leaving pills in your car on a 90°F day could expose them to temperatures well above 130°F. If your pills have been sitting in a hot car or direct sunlight for an extended period, they may be less effective even though they look normal. Condoms are similarly vulnerable to heat, which can weaken latex and shorten shelf life.
Body Weight and Emergency Contraception
For daily birth control methods like the pill, IUD, or implant, body weight has not been shown to meaningfully reduce effectiveness. But for emergency contraception (the morning-after pill), weight matters considerably.
Research has found that the most common morning-after pill becomes significantly less likely to work in women with a BMI above 26, which corresponds to roughly 150 to 160 pounds depending on height. A different type of emergency contraceptive pill may also be affected by weight but to a lesser degree, making it a better option for women with a higher BMI. The copper IUD, when used as emergency contraception within five days of unprotected sex, is not affected by body weight and remains the most reliable emergency option regardless of size.
What Actually Drives Most Failures
For user-dependent methods like the pill, the 30-fold gap between perfect use (0.3%) and typical use (9%) tells the real story. Most contraceptive failures aren’t caused by the method breaking down. They’re caused by the difficulty of following a precise daily routine for months and years at a time. Forgetting a pill, picking up a refill late, not realizing a medication interaction exists, or storing pills improperly are all small, common lapses that add up over a full year of use.
If you want the lowest possible chance of an unintended pregnancy without relying on daily habits, long-acting methods offer failure rates under 1%. If you prefer the pill, patch, or ring, using them as consistently as possible and knowing the timing rules for missed doses are the most practical ways to close the gap between that 9% and 0.3%.