Health & Fitness Calculators
Conception Calculator
Estimate ovulation and the fertile window.
FreeNo sign-upWorks in your browser
Estimated ovulation / conception
Sun, July 26, 2026
Most fertile window
Tue, July 21, 2026 – Sun, July 26, 2026
Estimated due date if conceived
Sun, April 18, 2027
About the Conception Calculator
Enter the first day of your last period and your average cycle length and the calculator estimates your ovulation date, your most fertile window (the five days before ovulation through ovulation), and the resulting due date if you conceive. It's a helpful planning tool for those trying to conceive.
How to use the Conception Calculator
- 1Enter your first day of last period and average cycle length.
- 2Read the result instantly — it recalculates as you type.
- 3Adjust the numbers to model different scenarios.
Frequently asked questions
When is the fertile window?
The five days before ovulation plus ovulation day. Ovulation is estimated as cycle length minus 14 days after the period starts.
How accurate is it?
Cycle-based estimates are approximate. Ovulation predictor kits and basal body temperature tracking pinpoint it more precisely.