Most birth control pills start to reliably prevent pregnancy within 7 days, but some can work sooner depending on when you start them and what type they are.

Key timeframes

• Combination pill (estrogen + progestin) :
  • If you start within 5 days of the first day of your period, you are protected right away or within the first day. Backup is usually recommended for up to 7 days if started at any other time in your cycle.

* Many doctors still advise using condoms or another method for the first 7 days just to be safe.

• Progestin‑only “mini‑pill” :
  • Often effective within 48 hours (2 days), but if started later in the cycle or if you have a short cycle, you may need 2 days of backup protection.

* It must be taken at the same time every day, with very little leeway, to stay effective.

Practical advice

• Use condoms or avoid penis‑in‑vagina sex for at least the first 7 days after starting any pill unless a clinician has specifically told you you’re protected sooner.

• If you miss pills, vomit soon after taking one, or have severe diarrhea, effectiveness can drop and you may need backup or emergency contraception depending on the situation.

• If you’re unsure which pill you’re on or when to consider yourself protected, contact a healthcare provider, clinic, or pharmacy for personalized guidance.