Already pregnant? Enter your due date or current week to estimate when conception likely happened.

How to Use the Pregnancy Conception Calculator

Toggle between "Due Date" and "Current Week of Pregnancy," depending on which you know, enter that one value, and the calculator estimates when conception likely happened.

This is a narrower tool than the standalone Conception Calculator, and deliberately so. That one is built for anyone curious about conception timing, including people who aren't pregnant yet and are working from cycle-tracking assumptions. This one assumes you're already pregnant and already know a due date or a current week — it's for working backward from what a doctor or a pregnancy test has already told you, not for planning-stage estimates.

Conception date = Due date − 266 days
Conception date = (Today − current week × 7 days) + 14 days

Both routes land on the same 266-day-before-due-date relationship the standalone calculator uses — there's no different math here, just a different starting point. The current-week mode is really just a shortcut: it reconstructs an implied last-period date from how far along you say you are, then applies the same 14-day offset to conception that every other calculator on this site uses.

Expect a date, not a certainty. Ovulation timing varies enough between cycles that "266 days before the due date" is a well-supported average, not a fixed biological rule that applies identically to everyone. The due-date mode tends to be the more reliable of the two, since a due date usually already reflects any clinical adjustment a doctor made from an early ultrasound; the current-week mode instead trusts your own count of how far along you are, which carries whatever rounding was already baked into that number. Not yet pregnant and thinking about cycle-based conception timing for planning purposes? The standalone Conception Calculator is the more appropriate tool — this one only makes sense once a pregnancy is already confirmed.

This is an estimate, not a precise determination. It's built on the same population-average timing every due-date and conception calculator on this site uses — actual ovulation and conception timing vary by individual and by cycle. Treat the result as a reasonable range to think in, not an exact date to rely on.