Estimate your ovulation date and fertile window from your last period and cycle length for family planning.
Ovulation Calculator
Health
Inputs
How useful was this tool?
Enter the first day of your last menstrual period.
Enter your average cycle length in days (most cycles are 28 days).
Click Calculate to see your ovulation date and fertile window.
Ovulation usually occurs about 14 days before your next period. The fertile window spans roughly 5 days before ovulation through 1 day after, since sperm can survive up to 5 days and the egg lives ~24 hours. This is an estimate — real cycles vary. For birth control, do not rely on this alone.
It estimates ovulation as 14 days before your next period. Real ovulation can vary by several days. Tracking basal body temperature, cervical mucus, or ovulation test kits improves accuracy.