Plan B (the levonorgestrel “morning‑after pill”) should be taken as soon as possible after unprotected sex, and always within 72 hours (3 days) for it to work effectively in preventing pregnancy. It is for emergencies only, not regular birth control.

Quick Scoop

  • Best timing: Take Plan B right away , ideally within 12–24 hours after unprotected sex; effectiveness is highest in this window.
  • Maximum window: It can be taken up to 72 hours (3 days) after unprotected sex; after that, it is not recommended because effectiveness drops significantly.
  • What it does: It works mainly by delaying ovulation so that an egg is not released and sperm cannot fertilize it; it does not end an existing pregnancy and is not an abortion pill.
  • When to consider it:
    • No birth control was used during penis‑in‑vagina sex
    • A condom broke, slipped off, or leaked
    • You missed pills or used another method incorrectly
    • You are worried your usual birth control failed in some way

Mini Timing Breakdown

  • 0–24 hours after sex: Highest effectiveness ; some data suggest up to about 95% effectiveness when taken in this time frame.
  • 24–48 hours: Still effective but somewhat less than in the first 24 hours; you should still take it.
  • 48–72 hours: May still prevent pregnancy and is still recommended if within this window, but protection is lower than earlier.

If more than 72 hours (3 days) have passed, levonorgestrel Plan B is no longer advised; in some countries another pill (ulipristal acetate) can be used up to 120 hours (5 days), or a copper IUD can be considered as emergency contraception, so a healthcare professional or clinic should be contacted urgently in that situation.

Key Safety Notes

  • Plan B is generally safe for most people and is available over the counter without a prescription or age requirement in many places.
  • It is not intended as a regular birth control method; if you find yourself needing it often, a provider can help you choose a more reliable ongoing method.
  • If you vomit within 2 hours of taking it, speak to a clinician; you may need another dose. (This is a standard emergency‑contraception caution, and many product leaflets advise this.)
  • If your period is more than about a week late after taking Plan B, or you have pregnancy symptoms, take a pregnancy test and consult a healthcare professional.

Bottom line: Take Plan B as soon as you can after unprotected sex, and no later than 72 hours. If you are outside that window, contact a clinic or healthcare provider immediately to ask about other forms of emergency contraception.

Information gathered from public forums or data available on the internet and portrayed here.