Ovulation Calculator
Fertile window & ovulation date
| Period starts | Fertile window | Ovulation |
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Predictions assume a regular cycle and ovulation about 14 days before the next period. Cycles vary, so don't rely on this for contraception. See a doctor about very irregular or painful periods.
About Ovulation Calculator
Trying to conceive? Your chances are highest in the fertile window: the five days before ovulation, ovulation day and the day after. Enter the first day of your last period and your usual cycle length to see your ovulation date and fertile days for the next six cycles, marked on a calendar.
- Pick the first day of your last period.
- Enter your average cycle length.
- Read your ovulation date and fertile window, and see them on the calendar.
Frequently asked
When am I most fertile?
In the two or three days before ovulation and on ovulation day itself. Ovulation is usually about 14 days before your next period: day 14 of a 28-day cycle, day 18 of a 32-day cycle.
How accurate is an ovulation calculator?
It's a good estimate for regular cycles, but ovulation can shift by a few days from month to month. Ovulation test kits, basal body temperature and cervical mucus changes can confirm it.
When should I see a doctor?
If you're under 35 and haven't conceived after a year of trying, or over 35 after six months, or sooner if your periods are very irregular.
Is what I type sent to a server?
No. The tool runs entirely in your browser and there's no server behind it, so what you type never leaves your device and nothing is stored. You can check: it keeps working if you go offline after the page has loaded.
More from the Calculators drawer
Other tools kept in this drawer, plus a few favourites from the bench.