Ovulation Calculator
Estimate ovulation day and fertile window from LMP and cycle length.
Input Data
First day of the last period.
Average cycle length in days.
Results
2026-01-15
2026-01-10
2026-01-17
Ovulation 2026-01-15; fertile 2026-01-10 to 2026-01-17.
At a glance:Ovulation ≈ LMP + (cycle − 14) days; fertile window ≈ LMP + (cycle−19) to LMP + (cycle−12) days.
Formula
Ovulation = LMP + (cycle − 14).
Fertile = LMP + (cycle−19) ~ LMP + (cycle−12).
How to Use
- Enter LMP and cycle length.
- The tool returns ovulation day and fertile window.
Case Studies
LMP 2026-01-01, 28-day → ovulation 2026-01-15
Ovulation = 1/1 + 14 = 1/15; window 1/10–1/17.
FAQ
Accurate?
Estimate; actual ovulation varies.
Irregular cycles?
Uses average cycle; less precise.
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References
Content reviewed by the Calculatorism editorial team. Results are for reference only; please refer to the relevant authorities for the official figures.