Calculate Due Date

Calculate your baby's estimated due date using Naegele's rule.

First day of last period

Cycle length (days)

How is the due date calculated?

The due date is calculated using Naegele's rule: First day of last period + 280 days (40 weeks). If your cycle is shorter or longer than 28 days, the difference is taken into account.

Only about 4% of babies arrive on their due date. Most are born within a window of 2 weeks before to 2 weeks after the date.

This calculator does not replace a medical calculation. The actual date is confirmed by ultrasound.