Ovulation Calculator
Estimate ovulation date and fertile window from the last period start date and average cycle length.
Inputs
Result
Enter values on the left and select Equals to see the result here.
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What the Ovulation Calculator does
- Estimates ovulation date using an average cycle length approach.
- Provides a fertile window around the estimated ovulation date.
How to use the Ovulation Calculator
- Enter the start date of your last period.
- Enter your average cycle length in days.
- Click Calculate to see estimated dates.
Formula / methodology used
- Assumes ovulation occurs roughly 14 days before the next period.
- Fertile window is estimated as 5 days before ovulation through 1 day after.
Example calculation
Last period: 2026-03-01, cycle length: 28 days.
- Ovulation ≈ start + (28 − 14) days
- Compute fertile window around ovulation
Result: Outputs ovulation date and fertile window start/end.
Ovulation Calculator FAQs
How accurate is this estimate?
It’s a planning estimate. Individual cycles vary, and ovulation can shift month to month.