Pregnancy Due Date Calculator
Due date, gestational age and trimester.
Enter the first day of your last period to see the estimated due date.
Uses Naegele’s rule (last period + 280 days, adjusted for cycle length). This is an estimate — only about 4% of babies arrive on the exact due date. Not medical advice; confirm with your healthcare provider.
How to use the Pregnancy Due Date Calculator
- 1 Enter the first day of your last menstrual period.
- 2 Adjust your average cycle length if it differs from 28 days.
- 3 See your estimated due date, how far along you are and your trimester.
Examples
- ▸ A last period starting Jan 1 with a 28-day cycle gives a due date around Oct 8 (280 days later).
Frequently asked questions
How is the due date calculated?
It uses Naegele's rule: 280 days (40 weeks) from the first day of your last period, adjusted for cycle lengths other than 28 days.
How accurate is it?
It is an estimate — only about 4% of babies are born on the exact due date, and most arrive within two weeks either side. An ultrasound dating scan is more precise.
Is my data private?
Yes. Everything is calculated in your browser; no dates are uploaded or stored anywhere.