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Ovulation Calculator

Estimate your ovulation date and fertile window from your last period and cycle length.

How this is calculated
Ovulation date = last period + (cycle length − 14 days). Fertile window = 5 days before to 1 day after ovulation.

Assumptions used in this calculation

  • Luteal phase: Assumes a standard 14-day luteal phase (time from ovulation to next period), which is fairly consistent even when cycle length varies.

About this calculator

The ovulation calculator estimates your ovulation date and fertile window (the days you're most likely to conceive) from the first day of your last period and average cycle length, combining what the master prompt lists as separate ovulation and conception calculators, since they use the same underlying date math.

Worked example

Last period Jan 1, 2026, 28-day cycle

Result: Ovulation ≈ Jan 15; fertile window Jan 10-16

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