Ovulation Calculator
Estimate your next ovulation day, 6-day fertile window and next period — from just your last period date and cycle length. Nothing leaves your device.
Find your fertile window
How the estimate works
Ovulation usually happens about 14 days before the next period — not 14 days after the last one, which is why cycle length matters. The fertile window spans roughly six days: the five days before ovulation (sperm survive up to five days) plus ovulation day itself (the egg lives about 24 hours). Calendar estimates work best for regular cycles; if yours varies a lot, ovulation test kits or temperature tracking are more reliable.
Frequently asked questions
When do I ovulate?
About 14 days before your next period — day 14 of a 28-day cycle, day 18 of a 32-day cycle.
How long is the fertile window?
About 6 days: five days before ovulation plus ovulation day.
How accurate are ovulation calculators?
Good estimates for regular cycles; tests and temperature tracking are more precise.