Pregnancy timing
Reverse Due Date Calculator
Work backward from a known due date to your last period, your conception date, and how far along you are.
Your details
The due date you want to work back from.
Calculated on your device. Your dates are never sent or stored.
Result
Enter your details to see your estimate. Every result is an estimate — your clinician sets the official due date.
How it works
A due date is 280 days after the first day of the last period and 266 days after conception, so a known due date can be turned back into those dates.
This is handy when you know the due date but not the original dating details.
See the full methodology and pregnancy term definitions on the main page.
The formula
last period = due date − 280 daysconception = due date − 266 days
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