Pregnancy calculator
Estimate due date and gestational age from the last menstrual period.
Formula
Due date = LMP + 280 days; gestational age = reference − LMP
First day of last period = 2026-07-01 · Reference date = 2026-10-12
How to use
- Enter the first day of your last period.
- Set the reference date for gestational age.
- Read estimated due date, weeks and remaining days.
Examples
- LMP January 1, 2025: due October 8, 2025.
- January 29 is 4 weeks after January 1.
Frequently asked questions
What cycle is assumed?
A regular 28-day cycle; irregular cycles can make this estimate unreliable.
Does this replace ultrasound dating?
No. Clinical and ultrasound assessment may establish a different due date.
Why is the reference date fixed?
It is an editable example so the page remains reproducible; set your actual date.
Sources
Updated: