Ovulation Calculator
Estimate your most fertile days for the next three cycles.
| Cycle 1: fertile window | Oct 20, 2026 to Oct 25, 2026 |
|---|---|
| Cycle 1: estimated ovulation | Sunday, October 25, 2026 |
| Cycle 2: fertile window | Nov 17, 2026 to Nov 22, 2026 |
| Cycle 2: estimated ovulation | Sunday, November 22, 2026 |
| Cycle 3: fertile window | Dec 15, 2026 to Dec 20, 2026 |
| Cycle 3: estimated ovulation | Sunday, December 20, 2026 |
| Next period expected | Sunday, November 8, 2026 |
How to use it
- Enter the first day of your last period.
- Enter your usual cycle length: the days from the start of one period to the start of the next. If it varies, use your average.
- Treat the dates as estimates. Ovulation tests or tracking temperature give a better read on your own cycle.
Formula
Next period = last period start + cycle lengthOvulation ≈ next period − 14 daysFertile window = the 5 days before ovulation and the day of ovulation (6 days)
Example
With a 28-day cycle and a last period starting October 1, 2026, the next period is expected Thursday, October 29, ovulation is estimated for Thursday, October 15, and the fertile window runs Oct 10 to Oct 15, 2026.
Questions
Why a 6-day window?
Sperm can survive several days and the egg about a day, so research on timing of intercourse found pregnancies came from the six days ending on ovulation day.
Can I use this as birth control?
No. Calendar estimates miss when ovulation shifts, which is common. Talk to a clinician about reliable contraception.
What if my cycles are irregular?
A calendar estimate is less reliable. Ovulation predictor kits and a clinician can help.
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Last reviewed 2026-10-11. Found a mistake? Tell us.