Ovulation Calculator
Estimate your most fertile days, your likely ovulation day and when your next period is due, for the next three cycles.
Find your fertile days
How the fertile window works
| Cycle length | Ovulation around | Fertile window |
|---|---|---|
| 24 days | Day 11 | Days 6–11 |
| 28 days | Day 15 | Days 10–15 |
| 32 days | Day 19 | Days 14–19 |
| 35 days | Day 22 | Days 17–22 |
How it is calculated
first day of last period + cycle length
next period − 14 days
the 5 days before ovulation + ovulation day
Day 1 is the first day of your period, so in a 28-day cycle ovulation falls around day 15 — 14 days after your period starts and 14 days before the next one. That 14-day gap is an average; it varies between women and from cycle to cycle.
In the study behind the six-day window, only about 30% of women had their whole fertile window within days 10 to 17 of the cycle — so ovulation tests or tracking body temperature give a more personal answer.
More health calculators
For general information only — not medical advice, diagnosis or treatment. These calculators use population formulas that cannot account for every individual, and are meant for adults unless stated. Always speak to a qualified doctor about your health, and never delay seeking care because of a result here.