Ovulation Predictor

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

✓ Reviewed by Dr. Poonam Sekhon Chahal · 24 May 2026

How this is calculated

Ovulation ≈ last period + (cycle length − 14). The fertile window spans the 5 days before ovulation plus the day after (sperm survive ~5 days, the egg ~1 day).

Sources

  1. Wilcox AJ, Dunson D, Baird DD. The timing of the 'fertile window' in the menstrual cycle. BMJ 2000.
This calculator is for educational purposes and is not a substitute for professional medical advice, diagnosis, or treatment. The result is based on standard clinical formulas applied to the values you entered — your individual situation may need adjustments your doctor can make. Never disregard professional medical advice or delay seeking it because of something you read or calculated on healthcalculus.