Plan Ahead With Transparent Fertility Estimates
Use this free tool to estimate your fertile window, predicted ovulation date, next period, and an estimated due date if conception occurs this cycle. You can optionally add an LH surge (ovulation test) date or BBT shift for more tailored results.
Important: This calculator is for education only and may be inaccurate for irregular cycles. Do not rely on it for contraception or medical decisions. Always consult a qualified healthcare professional.
Ovulation & Fertility Calculator
Use the first day of full flow.
Common range is 21–35 days; 28 is a typical default.
Often ~14 days; enter your known value if charting.
Accounts for irregularity; widens the fertile window.
Ovulation commonly follows ~24–36 hours after a positive test.
A sustained BBT rise typically indicates ovulation has already occurred ~1 day earlier.
Tip: Add LH/BBT data for stronger estimates.
Your Cycle Breakdown
| Item | Date / Range |
|---|---|
| Predicted Ovulation | — |
| Fertile Window (peak fertility near ovulation) | — |
| Next Period (estimate) | — |
| Estimated Due Date if Conceived | — |
These are estimates based on the dates you enter and typical cycle patterns. Individual cycles vary. This tool is not medical advice.
How we estimate
- Ovulation by cycle math: counts back the luteal length from your next expected period (LMP + cycle length).
- LH surge override (if provided): ovulation ≈ LH date + 1 day (bounded by your variability).
- BBT shift override (if provided): ovulation ≈ BBT date − 1 day (post-hoc confirmation).
- Fertile window: spans several days before ovulation and up to ovulation day; widened by your variability.
- Due date (EDD): estimates both by LMP (+280 days) and by ovulation/conception (+266 days) and displays the latter when LH/BBT is present.
At-a-Glance Summary
Predicted Ovulation
—
Fertile Window
—
Next Period (est.)
—
EDD if Conceived
—
Luke’s Picks Editorial
Last updated • Family planning tools & education.