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Ovulation Calculator
Estimate ovulation day and fertile window from cycle dates.
Inputs
Enter your values below.
Result
Your answer appears here.
Enter values and press Calculate — the result appears here.
How it works
The formula behind this calculator.
Ovulation ≈ LMP + cycleLength − 14 days; fertile window = ± 5 days
- LMP
- First day of last period
- cycleLength
- Average cycle length in days
Ovulation happens 14 days *before* the next period, not 14 days after the last one. The fertile window is ~5 days before to 1 day after ovulation.
Example: LMP Jan 1, 28-day cycle → ovulation around Jan 14
Ref: ACOG guidelines
Tips
- 💡 Ovulation typically happens 14 days before your next period, not 14 days after your last one.
- 💡 Use basal body temperature or LH test strips for the most accurate timing.