Ovulation Calculator
Predict your ovulation day and fertile window based on cycle data.
The Ovulation Calculator estimates when you are most likely to ovulate based on your last period start date and cycle length. Ovulation typically occurs about 14 days before your next period.
Enter the day of your last period (as day of the month or day of year) and your average cycle length. The calculator identifies your estimated ovulation day and fertile window (5 days before to 1 day after ovulation).
The fertile window accounts for the fact that sperm can survive up to 5 days in the reproductive tract, while the egg is viable for about 12-24 hours after release. This gives a roughly 6-day fertile window per cycle.
Frequently Asked Questions
When does ovulation occur?
Ovulation typically occurs about 14 days before the start of your next period. For a 28-day cycle, this is around day 14.
What is the fertile window?
The 6-day period including the 5 days before ovulation and the day of ovulation itself. These are the days when conception is possible.
How can I confirm ovulation?
Ovulation predictor kits detect the LH surge 24-36 hours before ovulation. Basal body temperature rises 0.5-1 degree F after ovulation.