Ovulation Calculator

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Find your most likely ovulation day and fertile window from your last period, cycle length and luteal phase. Free and instant.

days
days
Days from ovulation to your next period (usually 12–16).
Estimated ovulation –
Fertile window –
Next period –
Next cycle ovulation –
Ovulation is estimated as your next period minus the luteal phase. The fertile window spans about five days before ovulation through the day after. An estimate only — not a contraceptive method.

About Ovulation Calculator

The ovulation calculator predicts your most likely ovulation day and fertile window from three inputs: the first day of your last period, your average cycle length and your luteal phase. It also projects your next period and the ovulation date of the following cycle.

The method is the standard calendar calculation: ovulation is estimated as your next period minus the luteal phase, which usually lasts 12 to 16 days. The fertile window spans about five days before ovulation through the day after, because sperm can survive several days while the egg is viable for roughly one.

It is a quick, free way to time conception attempts or simply understand your cycle. Everything runs instantly in your browser as you adjust the numbers.

How to use Ovulation Calculator

  1. Pick the first day of your last period in the date field.
  2. Set your average cycle length in days (28 is typical, but cycles vary).
  3. Adjust the luteal phase if you know yours — 14 days is the common default.
  4. Read the estimated ovulation date, fertile window, next period and next-cycle ovulation.

Frequently asked questions

The tool adds your cycle length to the first day of your last period to find the next period, then subtracts your luteal phase. With a 28-day cycle and 14-day luteal phase, ovulation lands around day 14.

The roughly six-day stretch when conception is most likely: about five days before ovulation through the day after it. The calculator highlights this range so you can plan around your most fertile days.

Calendar estimates are least reliable with irregular cycles, since they assume each cycle matches your average length. Tracking basal body temperature or using ovulation test strips gives a more direct signal in that case.

It is the span from ovulation to your next period, usually 12 to 16 days. Because it is relatively stable, the calculator counts backwards from the predicted period by this many days to place ovulation.

No — the results are estimates based on averages, not medical advice, and this is not a contraceptive method. Ovulation timing varies from cycle to cycle, so consult a healthcare provider for fertility planning.
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