IUDs are over 99% effective at preventing pregnancy, making them one of the most reliable forms of birth control available. In typical real-world use, fewer than 2 out of every 100 women using an IUD will become pregnant within a year. That puts IUDs in the same effectiveness tier as sterilization, but with the advantage of being fully reversible.
How IUDs Compare to Other Birth Control
The typical-use failure rate for IUDs sits at roughly 0.8% per year in the United States, and around 1.4% globally across 43 countries studied. For context, the pill, patch, and ring all have typical-use failure rates closer to 7-9% per year, mostly because they depend on you remembering to take or replace them on schedule. IUDs work passively once inserted, which eliminates the most common reason birth control fails: human error.
Continuation rates tell a similar story. About 86% of people using long-acting methods like IUDs are still using them after 12 months, compared to just 55% of pill users and 49% of patch users. People stick with IUDs longer partly because there’s nothing to remember daily or weekly, and partly because satisfaction tends to be high once the adjustment period passes.
Copper vs. Hormonal: Both Over 99% Effective
Every IUD currently on the market, whether copper or hormonal, prevents pregnancy at a rate above 99%. The brands differ in how long they last and what side effects to expect, but not in how well they work.
- ParaGard (copper): Approved for up to 10 years. Contains no hormones. Works by triggering a localized inflammatory response inside the uterus that is toxic to sperm, preventing them from moving normally or surviving long enough to reach an egg.
- Mirena (hormonal): Approved for up to 5 years. Releases a small amount of progestin that thins the uterine lining and thickens cervical mucus, creating a barrier that sperm can’t easily pass through.
- Kyleena (hormonal): Approved for up to 5 years. Works the same way as Mirena but releases a lower dose of hormone, which some people prefer.
- Liletta (hormonal): Approved for up to 3 years. Similar mechanism and hormone level to Mirena.
- Skyla (hormonal): Approved for up to 3 years. The smallest hormonal IUD, originally designed with younger or nulliparous users in mind.
The choice between copper and hormonal usually comes down to side effects rather than effectiveness. Copper IUDs can make periods heavier and crampier, especially in the first few months. Hormonal IUDs typically lighten periods over time, and some people stop getting periods altogether. Neither type affects long-term fertility after removal.
When Protection Starts
The copper IUD works immediately. You’re protected from the moment it’s placed, no backup method needed. Hormonal IUDs are a bit different. If one is inserted during the first five days of your period, or as a direct swap when your old IUD expires, protection is immediate. If it’s placed at any other time in your cycle, you’ll need to use condoms or avoid vaginal sex for seven days while it takes effect.
The copper IUD also doubles as emergency contraception. When inserted within 120 hours (five days) of unprotected sex, it prevents pregnancy more than 99% of the time, making it the most effective emergency contraceptive option available. Unlike emergency contraceptive pills, it then stays in place and continues working as ongoing birth control for up to a decade.
What Can Reduce Effectiveness
The main thing that makes an IUD less effective is if it moves out of position or falls out entirely. This is called expulsion, and it happens at a rate of about 15 per 1,000 person-years of use. That means in any given year, roughly 1-2% of IUD users will experience a partial or complete expulsion.
Several factors increase expulsion risk. Heavy menstrual bleeding is the strongest predictor, particularly if it’s a recurring issue rather than a one-time event. Being 24 or younger, having had four or more pregnancies, and having a higher body weight are also associated with greater risk. Painful periods alone, interestingly, don’t independently raise expulsion risk once heavy bleeding is accounted for.
You can check that your IUD is still in place by feeling for the thin strings that hang through the cervix. If the strings feel significantly shorter or longer than usual, or if you can feel the hard plastic of the device itself, the IUD may have shifted. A displaced IUD won’t protect you reliably, so using backup contraception until you can get it checked is a good idea.
Effectiveness Over Multiple Years
IUD effectiveness holds up well over time, though it does decline slightly. Across 43 countries, the median cumulative failure rate for IUDs was 1.4% at 12 months, 1.9% at 24 months, and 2.1% at 36 months. That gradual increase is small, and much of it likely reflects undetected expulsions rather than the device itself becoming less effective. A properly positioned IUD remains highly reliable throughout its approved lifespan.
For hormonal IUDs, the hormone level does decrease over time, which is why each brand has a defined duration. Using a hormonal IUD beyond its approved timeframe could reduce its contraceptive effect. Copper IUDs maintain their mechanism regardless of time since the copper itself doesn’t deplete at a meaningful rate over 10 years.
Who Can Use an IUD
IUDs are safe for most people, including teenagers and those who have never been pregnant. Both the American College of Obstetricians and Gynecologists and the American Academy of Pediatrics endorse IUDs for adolescents. The outdated idea that IUDs are only appropriate for people who’ve already had children has been firmly set aside by current guidelines, which classify IUD use in young and nulliparous people as a category where the advantages clearly outweigh the risks.
IUDs can also be placed immediately after giving birth, before leaving the hospital. This is considered a best practice for preventing unintended pregnancies that occur in the months after delivery, a period when many people aren’t yet thinking about contraception but fertility can return quickly. Expulsion rates are somewhat higher with immediate postpartum placement, but the trade-off in convenience and protection is generally considered worthwhile.