How to use the Due Date Calculator
Enter the first day of last period, average cycle length and as of date and the result appears straight away. Everything runs in your browser, so nothing you type is uploaded.
How it works
Naegele's rule: last period + 280 days
Examples
- Last period 1 Sep 2026, 28-day cycle
Estimated due date: Tue, June 8, 2027 Gestational age: 10 weeks 0 days (trimester 1) Days to go: 210 End of first trimester (13 weeks): Tue, December 1, 2026
- Last period 1 Oct 2026, 28-day cycle
Estimated due date: Thu, July 8, 2027 Gestational age: 5 weeks 5 days (trimester 1) Days to go: 240 End of first trimester (13 weeks): Thu, December 31, 2026
Limitations and assumptions
Estimate only. Your healthcare provider will confirm dates with a scan. General estimate for adults, not medical advice. Speak to a doctor or registered dietitian before making significant changes to diet, exercise or health routines.
Frequently asked questions
How is the due date worked out?
Add 280 days to the first day of your last period (Naegele's rule), adjusting for cycle length.
How accurate is it?
Only about 4 to 5 percent of babies arrive on the due date; most come within two weeks either side.
Will an ultrasound change it?
Possibly. Your midwife or doctor may revise the date from an early scan.
What if I know my conception date?
Conception is typically about two weeks after the last period starts, in a 28-day cycle.