Period & Ovulation Calculator – Track Cycle & Fertile Days

How this works

Ovulation usually happens about 14 days before your next period, not 14 days after the last one. So we count back 14 days from each predicted period. Your fertile window is the 5 days before ovulation plus the day of ovulation, because sperm can survive up to 5 days.

Good to know

• This is a prediction. Cycles shift with stress, illness, travel and breastfeeding.
• Do not use it as contraception.
• See a doctor if your cycle is often shorter than 21 or longer than 35 days, your periods stop for 3+ months, or you bleed between periods.