Ovulation Calculator — Fertile Days
Trying to conceive? Enter the first day of your last period and your usual cycle length to see your most fertile days for the next few months.
Updated
For general information only — not medical advice. Consult a doctor or registered dietitian before making health decisions.
Formula
Ovulation ≈ Next period − 14 days
Fertile window = 5 days before ovulation to 1 day after
Sperm can survive up to 5 days and an egg about 24 hours, which defines the fertile window.
Examples
Period started 1 Oct 2026, 28-day cycle
Likely ovulation 15 October 2026 · fertile window 10 Oct 2026 – 16 Oct 2026
30-day cycle
Likely ovulation 17 October 2026 · fertile window 12 Oct 2026 – 18 Oct 2026
Important information
- Ovulation tests (LH strips) and tracking basal body temperature can confirm the timing more precisely than a calendar estimate.
Frequently asked questions
When am I most fertile?
In the two days before and on the day of ovulation.
Can I use this to avoid pregnancy?
No. Calendar estimates are not reliable as contraception because ovulation timing varies.
What if my cycles are irregular?
Use your average cycle length, but expect less accurate dates. Ovulation tests help with irregular cycles.
Learn more
- Pregnancy Due Date: How It Is Calculated — How doctors estimate your due date from your last period, why pregnancy is counted as 40 weeks, how cycle length changes it, and what the trimesters mean.
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