You're counting the hours. It’s been roughly 96 hours since that "oh no" moment, and now you’re staring at the pharmacy shelf or scrolling through your phone wondering: can I take Plan B 4 days after the fact?
The short answer is yes, you can physically swallow the pill. Nobody is going to stop you. But the real question you're asking is whether it will actually do anything to prevent a pregnancy at this stage.
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Honestly, Plan B is a bit of a race against the clock. By day four, the engine is cooling down. While the packaging says it works best within 72 hours, life doesn't always happen in neat three-day windows. Sometimes you can't get to a clinic. Sometimes you just flat-out forgot until your brain did a frantic reboot on Tuesday morning. We’ve all been there.
The science of the 72-hour window
Plan B One-Step and its generic cousins (like Take Action or My Way) use a hormone called levonorgestrel. It’s basically a high dose of the same stuff in many birth control pills. Its primary job is to act like a biological "stop" sign for your ovaries. If you haven't ovulated yet, it tries to delay that egg release so the sperm—which can hang out in your reproductive tract for up to five days—don't have anything to meet up with.
The drop-off is real. Clinical data from the World Health Organization (WHO) and other major health bodies suggests that levonorgestrel is about 95% effective if taken within 24 hours. By the time you hit the 48-to-72-hour mark, that number dips significantly.
Once you hit day four (96 hours), the efficacy of Plan B is, frankly, questionable. It isn't zero, but it isn't something most doctors would bet on.
Why day four is different than day one
Think of it like trying to catch a train. On day one, the train is still at the station. By day four, the train has likely left, and you're just running down the tracks with your luggage. If you have already ovulated in those intervening days, Plan B is basically useless. It does not terminate an existing pregnancy. It doesn’t "undo" fertilization if it has already happened.
It's also worth noting that body weight matters more than people think. Studies, including research highlighted by the FDA, suggest that levonorgestrel might be less effective for individuals weighing over 165 pounds or with a BMI over 25. If you're at the four-day mark and in a higher weight bracket, the "standard" Plan B is probably not your best bet.
Better options for when you've waited 4 days
If you are specifically asking can I take Plan B 4 days after because that's the only brand you know, you should know there's a more powerful "sister" pill called Ella (ulipristal acetate).
Ella is different. It’s a prescription medication, which makes it a bit more of a hassle to get, but it is specifically designed to work for up to 120 hours (5 days) after unprotected sex. Unlike Plan B, which starts losing its punch after day three, Ella maintains a much more consistent level of effectiveness right up to that five-day cutoff.
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If I were in your shoes and it had been four days, I wouldn't waste my money on the $50 box of Plan B at the drugstore. I'd be calling a telehealth provider or a local Planned Parenthood to get an Ella prescription.
The Copper IUD: The "Gold Standard" emergency move
Most people don't think of an IUD as emergency contraception, but it’s actually the most effective thing we have. If you get a copper IUD (ParaGard) or even certain hormonal IUDs (like Mirena or Liletta) inserted within five days of unprotected sex, the failure rate is less than 0.1%.
It’s a bit more invasive, sure. You need a doctor to move things around. But it works regardless of your weight, and it stays in your body to prevent pregnancy for years afterward. If you’re at the 96-hour mark, this is the "nuclear option" that actually works.
What about the side effects on day four?
If you do decide to take Plan B late, prepare for your cycle to get a little weird. You might feel nauseous. Your next period could be a week late, or it could come early and be weirdly heavy. This is the "hormone dump" effect.
Because you're taking it late, the anxiety of waiting for that period is going to be ten times worse. You'll be hyper-aware of every cramp. Just know that Plan B side effects often mimic early pregnancy symptoms, which is a cruel joke of biology.
Real-world efficacy and the "Maybe" factor
Is there a chance it works? Sure. If your ovulation was naturally scheduled for day six or seven of your cycle, taking Plan B on day four might still catch the window and delay the egg. But you’re gambling.
Medical experts at the Mayo Clinic and ACOG generally emphasize that while taking levonorgestrel up to five days out is technically allowed, it’s not recommended because of how much the success rate plunges. You’re essentially paying full price for a significantly diminished result.
Actionable steps for your next 24 hours
Stop staring at the clock and do these three things right now:
- Check your cycle calendar. If you know for a fact you ovulated a week ago, emergency contraception might not even be necessary (though counting days is notoriously unreliable). If you are right in the middle of your cycle, the risk is at its peak.
- Call for Ella. Skip the over-the-counter aisle. Contact a service like Nurx, PRJKT RUBY, or a local clinic. Tell them specifically that you are at the 96-hour mark. They will prioritize getting you a prescription for ulipristal acetate because they know Plan B is likely to fail now.
- Get a pregnancy test for later. No test will show a positive result today. It takes time for hCG to build up. Mark your calendar for 21 days from today. That is the only way to know for sure if your "late" Plan B attempt worked.
The reality of asking can I take Plan B 4 days after is that you are in a grey zone. It's better than doing nothing, but it's significantly worse than taking Ella or getting an IUD. If you have the choice, choose the option that was built for a five-day window. If Plan B is truly your only option—say, you're in a "contraceptive desert" and can't get a prescription—take it, but keep your expectations realistic and have a Plan B for your Plan B.
Check your local laws and clinic hours immediately. In many states, pharmacists can prescribe Ella directly without you having to see a primary care doctor first. That could be your saving grace today.