Ovulation Calculator
Find your likely ovulation day and fertile window from your last period and cycle length.
Inputs
Formula
- Ovulation = LMP + cycle − luteal phase
- Fertile window = ovulation − 5 days to ovulation + 1
The luteal phase (ovulation to next period) is fairly fixed at about 14 days, so ovulation is easier to predict backwards from the next period than forwards from the last one. Sperm survive up to five days, which is why the fertile window opens before ovulation.
Step-by-step calculation
- 1
Ovulation
LMP + cycle − luteal
Jan 15, 1970
Frequently asked questions
What does the Ovulation Calculator do?
Find your likely ovulation day and fertile window from your last period and cycle length. The Ovulation Calculator on OneCalcApp returns the result instantly as you type, together with the formula and the substituted values.
How do I use the Ovulation Calculator?
Enter your values in the input fields, choose the relevant units or options, and the Ovulation Calculator recalculates automatically. You can copy, print or export the result.
Is the Ovulation Calculator free to use?
Yes. The Ovulation Calculator is completely free, needs no sign-up and has no usage limit on OneCalcApp.
How accurate is the Ovulation Calculator?
It uses the standard formula Ovulation = LMP + cycle − luteal phase and full double-precision arithmetic, so results match a manual calculation to the displayed number of digits.
Does the Ovulation Calculator work on mobile and offline?
Yes. The Ovulation Calculator runs entirely in your browser on phones, tablets and desktops, and your inputs never leave your device.
Where can I find related tools?
OneCalcApp hosts 300+ calculators and converters, including the full Health collection. Related tools are linked at the bottom of every page.
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