Ovulation calculator.
Explore a possible ovulation date and fertile window from cycle assumptions.
Understand your cycle
Dates are estimates. Irregular cycles, recent hormonal contraception and uncertain period dates reduce reliability.
Calendar estimate only; it does not confirm ovulation. The window spans five days before through one day after estimated ovulation. Do not use these dates as contraception or as proof of safe days.
How this ovulation calculator works
The next period is estimated by adding your usual cycle length to the first day of the last period. The assumed luteal phase is subtracted to estimate ovulation. The displayed window extends from five days before through one day after that estimate.
A worked example
With a last period on 1 August 2026, a 28-day cycle and a 14-day luteal phase, the next period estimate is 29 August and ovulation estimate is 15 August. Real cycles can vary.
Can these dates identify safe days to avoid pregnancy?
No. A calendar estimate cannot confirm ovulation or reliable safe days. Do not use this calculator as contraception. Irregular cycles and changing cycle lengths make calendar estimates less reliable.
References and further reading
Calculations run on your device. Review your results before exporting or sharing them.