About this due date calculator
A due date calculator estimates the expected delivery date (EDD). This tool uses Naegele's rule: LMP + 280 days (40 weeks). Ultrasound dating may refine the estimate.
How to use
- Enter the first day of your last menstrual period.
- View estimated due date, gestational age, and trimester.
Formula
EDD ≈ LMP + 280 days (40 weeks)
Worked examples
Example: LMP on January 1 → estimated due date around October 8 (non-leap considerations aside).
Tips
- Only about 5% of babies arrive on the exact due date.
- This is not medical advice — confirm with your clinician.
Frequently asked questions
How accurate is a due date calculator?
It is an estimate. Cycles vary, and early ultrasound often provides a more precise dating window.