Fitness & Health

Reverse Due Date Calculator (Conception Date)

Work backward from an estimated due date to the likely conception date, last menstrual period, fertile window, and pregnancy timeline. It applies Naegele's rule in reverse with a cycle-length adjustment.

How to use

Enter the estimated due date.
Enter your average cycle length.
Check the fertile window and timeline.

Estimated due date (EDD)

Cycle length (days)

Cycle

Estimated conception date

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EDD − 280 days + (cycle − 14) ovulation offset

Fertile window

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LMP (estimated)

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Implantation (~)

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First positive test (~)

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Gestational age

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Estimates for general wellness, not medical advice. Check with a doctor or dietitian before acting on health figures.

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Common questions

How accurate is a reverse due date estimate?

It gives a probable range, since due dates are estimates and cycle length and ovulation timing vary between people.

What is Naegele's rule?

It is the standard method of estimating a due date by adding 280 days to the first day of the last menstrual period.