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Due date calculator

Due date calculator

Estimated due date —
Weeks pregnant today
—

Estimated with Naegele's rule (LMP + 280 days). It's only a guide: just 4% of births happen exactly on the due date. It's no substitute for medical follow-up.

This due date calculator estimates your estimated due date (EDD) and how many weeks pregnant you are today, from the first day of your last period.

Naegele’s rule

The estimate adds 280 days (40 weeks) to the first day of your last menstrual period. It’s a widely used starting point, not a precise prediction — an ultrasound dating scan and your healthcare provider’s follow-up remain the reliable sources.

FAQ

How is the due date calculated?
This tool uses Naegele's rule: it adds 280 days (40 weeks) to the first day of your last menstrual period (LMP).
How accurate is the estimated due date?
It's only a guide — only around 4% of births happen exactly on the estimated date. Most babies arrive within a couple of weeks before or after it.
What if I don't remember the exact first day of my last period?
Use your best estimate. For a more precise due date based on fetal measurements, an early ultrasound dating scan is more reliable than LMP alone.