Due Date Reverse Calculator

Work backward from a known due date to estimate your last menstrual period date, conception date, and when your second and third trimesters started or will start.

Google AdSense Banner

This area will contain advertisements after approval.

Google AdSense Banner

This area will contain advertisements after approval.

How It Works

Working backward from a due date

Due dates are conventionally calculated as 280 days (40 weeks) after the last menstrual period (LMP), so this calculator reverses that: subtracting 280 days from your due date to estimate your LMP. From there, it adds roughly 14 typical days to estimate a conception date, and adds 13 and 27 weeks respectively to estimate when the second and third trimesters began or will begin.

A reference tool, not a week-by-week tracker

Unlike our Pregnancy Week Calculator, this tool doesn't reference today's date at all, it's purely a reconstruction of your estimated pregnancy timeline from a single known due date. This is useful right after receiving a due date from a doctor or ultrasound and wanting to see the full estimated timeline at once, rather than tracking ongoing weekly progress.

Frequently Asked Questions

Why would I need to work backward from a due date?

If your due date came from an ultrasound rather than your own LMP tracking (common, and often considered more accurate, especially with irregular cycles), you may not have an exact LMP date on hand, this calculator reconstructs an estimate from the due date instead.

How accurate is the estimated conception date?

It's a typical estimate assuming conception occurred about 14 days after LMP, which is standard for an average cycle, but actual ovulation timing varies by individual and cycle, so treat this as an approximation.

Is this the same as the Pregnancy Week Calculator's due date mode?

They share the same underlying 280-day math, but this calculator focuses on reconstructing your full estimated timeline (LMP, conception, trimester start dates) as a reference, while the Pregnancy Week Calculator focuses on your current week, day and trimester relative to today.