Due Date Calculator
Estimate your pregnancy due date from your last menstrual period (LMP) using Naegele's rule.
Reviewed by the WorldCalcs team · Methodology · Last reviewed: June 2026
Estimated due date
8 October 2026
Gestational age: 23 weeks 0 days · 2nd trimester
What is a due date calculator?
A due date calculator estimates when a baby is likely to be born, based on the first day of the last menstrual period (LMP). A full-term pregnancy is counted as about 40 weeks (280 days) from the LMP.
How it's calculated
This tool uses Naegele's rule: it adds 280 days to your LMP, adjusting for your cycle length if it differs from 28 days. Example: an LMP of 1 January 2026 gives an estimated due date of 8 October 2026.
All calculations happen in your browser. Nothing is sent, stored, or tracked.
Results are estimates and may contain errors — for general information only, not professional advice. Always verify before relying on them. Disclaimer
How to use
Enter the first day of your last menstrual period and, if you know it, your average cycle length. The tool returns the estimated due date, current gestational age and trimester.
This estimate is informational only. An early ultrasound or your clinician's assessment is more accurate.
Frequently asked questions
How is a due date calculated?+
How accurate is a due date?+
What if my cycle isn't 28 days?+
Can an ultrasound change my due date?+
References
- Naegele's rule — estimated due date is about 280 days (40 weeks) from the first day of the last menstrual period (standard obstetric method).