If you’ve had unprotected sex around the time of ovulation, you still have options to prevent pregnancy, but which one works best depends on exactly where you are in your cycle and how quickly you act. The most important thing to know: not all emergency contraception works equally well once ovulation is underway. Your best option shifts depending on whether ovulation has already happened or is about to.
Why Timing Around Ovulation Matters So Much
Your fertile window spans roughly six days: the five days before ovulation plus the day of ovulation itself. Sperm can survive in the reproductive tract for up to five days, while an egg survives only about 24 hours after release. That means sex during this window carries the highest chance of pregnancy, and it’s also the window where some emergency contraception methods start losing their edge.
Most emergency contraceptive pills work primarily by delaying or blocking ovulation. If the egg has already been released, a pill that works by postponing ovulation has nothing left to postpone. This is the core challenge of preventing pregnancy during ovulation specifically, and it’s why knowing your options matters.
Levonorgestrel: The Over-the-Counter Pill
Levonorgestrel (sold as Plan B and similar brands) is the most widely available emergency contraceptive pill. It’s available without a prescription and without age restrictions in the United States. It works by delaying ovulation, and it’s highly effective when taken before ovulation occurs.
Here’s the catch: levonorgestrel loses most of its effectiveness once the hormonal surge that triggers ovulation has already begun. In a pilot study tracking women who had intercourse during their fertile window, none of the women who took levonorgestrel before or on the day of ovulation became pregnant, compared to an expected rate of about four pregnancies. But among women who took it after ovulation had already occurred, the number of pregnancies matched what would have been expected without any emergency contraception at all. In other words, once the egg is out, levonorgestrel provided little to no additional protection.
Levonorgestrel works best within the first three days (72 hours) after unprotected sex, and pregnancy rates climb noticeably when it’s taken at the four- to five-day mark. If you’re going to use it, take it as soon as possible. It may also be less effective for women with a BMI of 25 or higher.
Ulipristal Acetate: More Effective Near Ovulation
Ulipristal acetate (sold as ella) requires a prescription in the U.S. and represents a significant upgrade in effectiveness when you’re close to ovulating. While levonorgestrel can only delay ovulation when the hormonal trigger is still in its early stages, ulipristal can directly block the follicle from rupturing and releasing the egg even when hormone levels are already surging.
The difference is dramatic. When administered during the hormonal surge that precedes ovulation, ulipristal blocked ovulation in 79% of women. Levonorgestrel blocked it in just 14%, barely better than a placebo at 10%. This makes ulipristal the stronger choice if you suspect you’re right at the point of ovulating.
Ulipristal is effective for up to five days (120 hours) after unprotected sex, and unlike levonorgestrel, studies show its pregnancy prevention rates stay more consistent across that full window. It also performs better than levonorgestrel for women at higher body weights, though effectiveness may still decrease with higher BMI. The main barrier is access: you’ll need to contact a healthcare provider for a prescription, which can mean an office visit, telehealth appointment, or in some states, a pharmacist consultation.
One important limitation: if ovulation has already fully completed, ulipristal’s ability to help drops significantly, just as it does with levonorgestrel. It’s better at catching ovulation in its final moments, but it can’t undo an ovulation that’s already finished.
The Copper IUD: The Most Effective Option
A copper IUD is the most effective form of emergency contraception available, preventing pregnancy in more than 99% of cases when placed within five days of unprotected sex. Unlike pills, its primary mechanism doesn’t depend on blocking ovulation at all. Copper ions released by the device alter the environment inside the uterus and fallopian tubes, impairing sperm function and preventing fertilization. It can also affect the uterine lining in ways that make implantation less likely.
This distinction is critical for anyone who has already ovulated. Because the copper IUD works on sperm and the uterine environment rather than on the ovulation process, it remains highly effective even after the egg has been released. The CDC notes that when the day of ovulation can be estimated, a copper IUD can be placed more than five days after sex, as long as it goes in within five days of ovulation.
The tradeoff is logistical. You need a healthcare provider to insert it, which means scheduling an appointment quickly. The copper IUD also doubles as long-term contraception, lasting up to 10 years, so it’s worth considering if you want ongoing protection. Some people experience heavier periods and more cramping with a copper IUD, particularly in the first few months.
What About Hormonal IUDs?
Hormonal IUDs are not currently recommended as emergency contraception in U.S. guidelines. The 2024 CDC recommendations list only the copper IUD and three types of emergency contraceptive pills as approved options. If a hormonal IUD is placed more than seven days after the start of your period, you’d need to use backup protection (like condoms) for the next seven days. It won’t work retroactively to prevent pregnancy from sex that already happened.
Choosing Based on Where You Are in Ovulation
Your best move depends on timing:
- Before ovulation or early in the hormonal surge: Both levonorgestrel and ulipristal can work. Ulipristal is more effective, but levonorgestrel is easier to access without a prescription.
- Right before ovulation (hormonal surge already underway): Ulipristal is significantly more effective than levonorgestrel at this stage. If you can get a prescription quickly, it’s the better pill option.
- After ovulation has occurred: Neither pill offers reliable protection. A copper IUD is the only emergency method with strong evidence of effectiveness after the egg has already been released.
The challenge, of course, is that most people don’t know exactly when they ovulated. If you track your cycle with ovulation predictor kits or basal body temperature, you may have a reasonable estimate. Without that data, acting fast with the most effective method you can access gives you the best odds.
How Quickly You Need to Act
Every hour matters. All emergency contraceptive pills should be taken as soon as possible within five days of unprotected sex. Levonorgestrel’s effectiveness drops more steeply over time, with pregnancy rates climbing noticeably after three days. Ulipristal holds its effectiveness better through the full five-day window but still works best when taken early.
For a copper IUD, the five-day window from intercourse applies, with the additional flexibility of placement up to five days after estimated ovulation. Since scheduling an insertion takes time, call a provider or clinic immediately if you’re leaning toward this option. Many clinics and urgent care centers can accommodate same-day or next-day IUD placements for emergency contraception.
If you’re weighing your options and worried about the wait for a prescription, one practical approach is to take over-the-counter levonorgestrel right away while pursuing a copper IUD or ulipristal prescription. Having levonorgestrel on board early is better than waiting, though you should not take both levonorgestrel and ulipristal together, as they can interfere with each other.