Does Plan B work after three days?
Last updated September 3, 2026.
Plan B works best within 3 days of unprotected sex, can be taken up to 5 days, and loses effectiveness with every day you wait. Within the 3-day window, levonorgestrel pills reduce the chance of pregnancy by 75 to 89%. On days 4 and 5, it may still help, but the drop-off is real. If you are already past day 3, two options outperform it: ulipristal (ella), which holds effectiveness across all 5 days but needs a prescription, and the copper IUD placed within 5 days, which is the most effective emergency contraception and then keeps working as regular birth control. The single biggest variable is speed, so get whichever option you can get fastest. After taking Plan B, expect your period within about 3 weeks; if it does not come, take a pregnancy test. Use condoms or backup protection until your cycle restarts, because Plan B only covers the sex that already happened, not anything after.
What to do
- Take it immediately: within 3 days is the effective window, and sooner beats later.
- Days 4 to 5: ask about ella (prescription) or a copper IUD instead.
- Do not mix EC types: ella and Plan B within 5 days of each other can interfere.
- Test at 3 weeks: no period by then means take a pregnancy test.
- Backup after: Plan B protects against what already happened, not future sex.
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