LMP Apr 1, 2026, 28 day cycle
- Fertile window
- Apr 10, 2026-Apr 15, 2026
- Next period
- Apr 29, 2026
- Luteal phase
- 14 days
Ovulation Calculator
Use this free ovulation calculator to estimate ovulation date, fertile window, and next period from last period and cycle length.
Research-based formula Estimate limits shown Examples included Private history
Formula steps
- Estimate the next period from the last period date and cycle length.
- Subtract the luteal phase length to estimate ovulation.
- Show the fertile window as the five days before ovulation through ovulation day.
How to use the ovulation calculator
- Enter the requested measurements, dates, lab values, or workout details.
- Check that the units and formula assumptions match what the tool is asking for.
- Press the calculate button to see the answer, supporting metrics, and formula steps.
- Read the estimate with the health disclaimer in mind, then copy the result if you need it for notes.
Common uses
Estimate ovulation for regular cycles.
See the fertile window around ovulation.
Plan cycle tracking with a luteal phase assumption.
Avoid using calendar estimates as contraception.
Examples
Ovulation around day 14
Ovulation around day 16
Estimated window
Frequently asked questions
Quick answers about formulas, inputs, estimate limits, professional guidance, examples, and private in-browser history.
What can I use the Ovulation Calculator for?
Use it for quick educational estimates, planning, comparison, and trend checks. Health and fitness results should be interpreted with context, not as a diagnosis.
How does the Ovulation Calculator calculate the result?
The calculator estimates ovulation by subtracting luteal phase length from the next expected period date.
Is this medical advice?
No. This page provides an educational estimate only. Talk with a qualified health professional before making medical, pregnancy, nutrition, medication, or safety decisions.
Are my health inputs private?
Yes. The calculator runs in your browser tab. Recent answers stay only on the page while you use it and are not sent to a server.