Conception Date Calculator
Estimate your likely conception date from a due date or last period using this free conception date calculator that runs in your browser.
Enter details
Result
Enter a date to see your estimate.
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Choose to work from your last period or a due date.
- Enter the date.
- Read the estimated conception date and window.
How it works
Conception is about 14 days after the last period, or 266 days before the due date. A few-day window reflects sperm survival and ovulation timing.
Worked example
Due 8 Oct 2026. Estimated conception ≈ 16 Jan 2026.
Tips
- Estimate only — not medical advice. Dates and fertile windows vary between people and cycles; confirm with a healthcare professional.
Frequently asked questions
Can it pinpoint the exact day?
No — it gives a likely window; exact conception is rarely known.
Privacy?
Runs entirely in your browser. Your inputs are not saved or transmitted.
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Explore more in Family, Parenting & Custody.
Cite this tool
Zerdly. (2026). Conception Date Calculator. Retrieved from https://www.zerdly.com/tools/conception-date-calculator/
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.