You can take a Plan B pill up to 72 hours (3 days) after unprotected sex, but it works best the sooner you take it, ideally within 24 hours. After 72 hours, its effectiveness drops a lot, and another emergency option like the pill ella or a copper IUD may be recommended instead.

How late can you take Plan B?

  • Plan B (levonorgestrel 1.5 mg) is approved to be taken within 72 hours (3 days) after unprotected sex or birth control failure.
  • Its effectiveness is highest within the first 24 hours and decreases with each passing day.
  • Some sources note that levonorgestrel pills may still have some effect up to 120 hours, but this is less reliable and not how Plan B itself is labeled.

Simple rule of thumb: as soon as possible is much better than “by day 3.”

How well does Plan B work over time?

  • Taken within 24 hours: can reduce the chance of pregnancy by up to about 95% according to manufacturer and clinical summaries.
  • Taken within 72 hours: reduces risk by about 75–89% compared with no emergency contraception.
  • Plan B does not terminate an existing pregnancy; it mainly works by delaying ovulation so sperm and egg never meet.

If you were already ovulating at the time of sex, Plan B may not work as well, which is another reason timing matters.

What if it’s already been more than 72 hours?

If you’re past the 72‑hour mark, there are still options, but they’re different from Plan B.

  • Ulipristal acetate (ella)
    • Prescription-only emergency pill.
    • Can be used up to 120 hours (5 days) after unprotected sex and tends to work better than levonorgestrel later in the window.
  • Copper IUD
    • Can be placed up to 5 days after unprotected sex and is the most effective form of emergency contraception, with the bonus of long‑term birth control.

If you’re already past 72 hours, it is important to contact a clinic, telehealth service, or healthcare provider quickly to ask specifically about ella or a copper IUD.

Signs to watch for after taking Plan B

  • Your next period may come a little earlier or later, and flow can be lighter or heavier than usual.
  • Nausea, fatigue, breast tenderness, or mild spotting can happen for a short time.
  • If your period is more than about 1 week late after when you expect it, take a pregnancy test and follow up with a healthcare professional.

Quick FAQ style recap

  • How late can you take a Plan B pill?
    • Up to 72 hours after unprotected sex, but the sooner the better.
  • Is there anything after 3 days?
    • Yes: ella or a copper IUD can often be used up to 5 days after sex; these require seeing a provider.
  • Can I use Plan B as regular birth control?
    • No. It is meant only for emergencies, not as a primary method.

If you are in immediate need and unsure what to do, try to contact an urgent care clinic, sexual health clinic, or telemedicine service as soon as you can—timing really matters with all forms of emergency contraception.