Your ovulation day, fertile window and next period — in seconds.
The period date starts 12 days ago so you can see a sample result — change it to your own date.
Ovulation usually happens about 14 days before the next period starts. So this calculator adds your cycle length minus 14 days to the first day of your last period — for a 28-day cycle, ovulation lands 14 days after the period started.
The 6 days ending on ovulation day. Sperm can survive up to 5 days in the body, while the egg lives only about 12–24 hours after release, so the days just before ovulation count too. The 2–3 days right before ovulation are usually the most fertile.
It is an estimate based on average cycles. Stress, illness, travel and hormones can all shift ovulation by a few days, so use it as a guide — not as a guarantee, and not as a form of birth control.
With irregular cycles, a single average works less well. Enter your most common cycle length, track a few cycles, and consider ovulation test kits or temperature tracking for a clearer picture.