Health & Fitness
Ovulation Calculator
Estimate ovulation date and fertile window based on cycle length.
Formulas and edge cases are reviewed against authoritative references before publication. For methodology, editorial standards, or corrections, use the links below.
Frequently asked questions
How is ovulation estimated?
Ovulation is estimated as 14 days before the next period.
What is the fertile window?
The fertile window includes the days leading up to and just after ovulation.
Is this accurate for irregular cycles?
Accuracy may be lower for irregular cycles.
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About this tool
This Ovulation Calculator turns your inputs into practical results. Provide First day of last period and Cycle length to calculate Ovulation date and Fertile start.
Adjust values to compare scenarios and see how sensitive the result is. The calculation uses the numbers as entered, so double-check units and expect small differences from rounding in the displayed totals.