Overview
This tool estimates the due date from a reference date chosen by the user: the last menstrual period, conception date, or an ultrasound scan with the gestational age on that day. The result is an estimate for planning only.
Formula
Pregnancy is usually dated at 40 weeks (280 days) from the first day of the last period. If conception is known, 266 days is used. If gestational age at a scan is known, it is subtracted from 280.
How it works
Choose the method
Last period, conception date or ultrasound.
Enter the date
The reference date matching the method.
Review the estimate
The due date and current gestational age appear.
Worked examples
Last period on January 1
The estimated due date is around October 8 of the same year.
An eight-week scan
If the scan is on March 1 at eight weeks, add 32 weeks for the due date.
Frequently asked questions
Which method is most accurate?
A first-trimester ultrasound is often the most accurate; your clinician decides the official method.
Can the date change?
Yes, the clinician may adjust it based on fetal growth and further scans.
Does it work for multiple pregnancies?
It gives a general estimate, but multiple pregnancies need specialist follow-up and dates.
This calculator is for educational and informational purposes only and is not a substitute for professional advice.