How to use the Ovulation Calculator
The ovulation calculator predicts your fertile window and next period.
Open the Ovulation Calculator →
What you need to enter
- First day of last period
- Cycle length (days)
The formula
Ovulation ≈ day (cycle length − 14). The fertile window runs from 5 days before to 1 day after.
Worked example
Using the default values in the calculator:
- First day of last period: 2026-10-13
- Cycle length (days): 28
| Ovulation day | Tue, 27 Oct 2026 |
| Fertile window | Thu, 22 Oct 2026 – Wed, 28 Oct 2026 |
| Next period expected | Tue, 10 Nov 2026 |
| Pregnancy test from | Tue, 10 Nov 2026 |
Tips for better results
- Track several cycles for better accuracy.
- Ovulation tests can help.
Common mistakes to avoid
- Relying on it as contraception.
- Ignoring irregular cycles.
Please note: Health calculators and guides give general estimates, not medical advice. Talk to a doctor or other qualified professional about your own health. See our Disclaimer.