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Ovulation Calculator
Estimate your fertile window and the next three cycles from your last period and cycle length.
Fertile window and next cycles
Fertile window: —
Ovulation day: —
Luteal assumption: —
How to use the Ovulation Calculator
- Enter the first day of your last period.
- Set your average cycle length and period length.
- Adjust the luteal phase assumption if your cycle differs.
Features
- Fertile window from the last period date
- Next three cycles listed with dates
- Adjustable luteal phase assumption
- Period length used for each cycle
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Frequently Asked Questions
Common questions about the free online ovulation calculator.
Ovulation is placed a set luteal phase before the next period, and the fertile window runs
from five days before to one day after.
The tool assumes the luteal phase, the days after ovulation, lasts 14 days by default, and
you can set it from 9 to 16 days.
It lists the next three cycles with the fertile window, the ovulation day and the first day
of the next period for each.
A longer cycle moves ovulation later because the luteal phase stays fairly fixed while the
first half of the cycle varies.
No. It is an estimate for general information and not medical advice, and calendar methods
alone are not reliable contraception.
The calculator centres the window on the estimated ovulation day, with conception most likely
in the two days before it.
Calendar estimates are much weaker with irregular cycles. Tracking temperature or ovulation
tests gives better information.
No. Everything is calculated in your browser and nothing you enter is uploaded, saved or
shared.
Last updated: October 10, 2026