September 2026
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Ovulation calculator
Estimate ovulation date and the days where conception is most likely.
Estimate, not a diagnosis. This tool gives an educational estimate based on the numbers you enter. It cannot account for your individual health history — consult a healthcare professional for anything clinical.
How this works
We estimate ovulation by subtracting a typical luteal-phase length (14 days) from the expected next period. The fertile window is computed as the five days before ovulation plus ovulation day itself.
Inputs
- First day of last menstrual period
- Average cycle length (days)
Outputs
- Estimated ovulation date
- Fertile window range
Limitations & guidance
Estimates are population-level. Use ovulation tests (LH) or temperature charts for more personalized tracking. Consult a clinician for fertility concerns.
Related reading
- Understanding your cycle phases
- Luteal phase self-care guide
- Cycle variability: what the science says
- How age affects fertility
- GLP-1 medications and your period
Related tools
Frequently asked questions
How is ovulation calculated from my last period?
We subtract a typical luteal-phase length (14 days) from your expected next period date, which is your last period plus your average cycle length. That gives an estimated ovulation date.
How many days is the fertile window?
The fertile window is six days: the five days before ovulation plus ovulation day itself. Sperm can survive several days, and the egg is viable for about 24 hours after ovulation.
How accurate is an ovulation calculator?
It gives a population-level estimate, not a personalized prediction. Actual ovulation timing varies cycle to cycle. Ovulation predictor kits (LH tests) or basal body temperature charting are more precise for an individual cycle.