Estimated due date: How we calculate
How we calculate
We add 280 calendar days to the first day of the last menstrual period, the standard 28-day-cycle convention.
This is an estimate, not a predicted birthday. An early ultrasound can revise the clinical due date.
Worked example
The first day of the last menstrual period is 01.01.2026. Adding 280 days gives 08.10.2026. This is the model’s estimated due date, not a promised delivery date; cycle characteristics and ultrasound can change the clinical estimate.