You can start your pill on the first day of your next period, on the first Sunday after your next period starts, or any day (even immediately) if you’re sure you’re not pregnant. If you start your pill more than 5 days after your last period started, you must also use backup pregnancy protection (like condoms) until you have been on the pill for 7 straight days. After 7 days of being on the pill, you are protected from pregnancy and no longer need to use a backup method. The easiest way to figure out 5 days from the beginning of your period is to take the calendar date and add 4. For example, if your period started on Sunday the 10th, you would not require backup contraception if you started your pill by Thursday the 14th (that includes the 14th as a day that would provide you with immediate contraceptive coverage). However, birth control pills do not protect against STIs and you should always use a condom if you are not 100% sure of your partner’s STI status.