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
Common questions
Does Plan B work after three days?
Yes, but with a catch: Plan B is labeled for use as soon as possible within 72 hours (3 days) after unprotected sex, and that is when it works best. Taken within 3 days, levonorgestrel emergency contraception lowers the chance of pregnancy by 75 to 89%. You can take it up to 5 days after, and it may still help, but effectiveness drops with every day of delay, which is why the universal advice is take it now, not tonight. If you are already on day 4 or 5, Plan B is no longer the best tool. Ulipristal (ella) keeps its effectiveness steady across all 5 days (it is prescription-only), and a copper IUD placed within 5 days is the most effective emergency contraception of all, over 99%, with the bonus of becoming your ongoing birth control. Whichever route you take, the clock matters more than the brand. After taking Plan B, use backup contraception until your next period, and take a pregnancy test if your period has not arrived within 3 weeks. And if you need emergency contraception twice in a short window, stick with levonorgestrel the second time, since ella and Plan B taken within 5 days of each other can interfere.