Conception Calculator — From a Known Due Date or Birth Date

Conception Calculator

Work backward from a due date or birth date to estimate when conception happened.

Known due date or birth date

Works backward from a due date or actual birth date to estimate when conception most likely occurred.

Estimated conception date

Tuesday, April 14, 2026

Subtracts 266 days (38 weeks) from the due date — the typical gap between conception and a full-term birth. Actual timing varies, especially for babies born early or late.

A worked example

A due date of January 5, 2027 implies an estimated conception date of about April 14, 2026 — 266 days, or 38 weeks, earlier.

Frequently asked questions

How is this different from the Pregnancy Conception Calculator?

That tool works forward from your last period. This one works backward from a date you already know — a due date, or an actual birth date — which is useful after the fact rather than early in pregnancy.

Does it matter if the baby was born early or late?

Yes — this assumes a full 38-week (266-day) gap from conception to birth. A baby born early or late shifts the actual conception date earlier or later than this estimate suggests.

This calculator provides estimates for general informational purposes only and is not medical advice.