It depends on when you start taking them. You can take your first birth control pill any day of the month, but you may need a backup birth control method (like condoms) for the first 7 days.
Combination Pills (COCs)
If you start combination pills within 5 days after your period starts, you’ll be protected from
pregnancy right away. For example, if you get your period Monday morning, you can start the pill anytime until Saturday morning and be protected from pregnancy right away.
If you start combination pills any other time, you’ll be protected from pregnancy after 7 days of taking the pill. Use another method of birth control — like a condom or
female condom — if you have vaginal sex during the first week you’re on the pill.
Progestin-Only Pills (Mini Pills)
You can start progestin-only pills at any time. You’ll be protected from pregnancy after 48 hours (2 days). So use another method of birth control (like condoms) if you have vaginal sex during the first 48 hours.
Your nurse or doctor can help you figure out the best time to start your birth control pills, and when they’ll start working for you.