Health & Fitness Calculators
Ovulation Calculator
Estimate ovulation day, the fertile window, and the next period from the last period start date and average cycle length.
Quick guide
Enter the first day of your last period and your average cycle length. The calculator estimates the ovulation day, the fertile window around it, and the start of your next period; actual timing varies from cycle to cycle.
Read the full explanationHow It Works
Ovulation typically occurs about 14 days before the next period. Because sperm survive up to five days, the fertile window spans the five days before ovulation and about a day after.
Formula Used
Ovulation ≈ LMP + (cycle length − 14) days; fertile window ≈ ovulation − 5 days to ovulation + 1 day.
Example Calculation
With a 28-day cycle starting March 1, ovulation is estimated around March 15, with a fertile window of roughly March 10–16.
Practical Use Cases
- Identify the most fertile days when trying to conceive.
- Anticipate the next period.
- Understand your cycle timing.