Due Date Calculator
Estimate your pregnancy due date from the first day of your last menstrual period, using Naegele's rule.
- Free to use
- Accurate results
- No registration required
- Works on all devices
Your result
08-03-2027
Estimated due date
AI explanation
Formula
Due date = last period date + 280 days (Naegele's rule)Worked example
LMP 2026-01-01
| Field | Value |
|---|---|
| First day of last menstrual period | 01-01-2026 |
| As of date | 01-01-2026 |
| Estimated due date | 08-10-2026 |
Assumptions
- Uses Naegele's rule (280 days / 40 weeks from the last menstrual period), which assumes a regular 28-day cycle with ovulation on day 14.
- Informational only — always confirm dates with your healthcare provider, especially if an ultrasound-based due date differs from this estimate.
Frequently asked questions
How is my due date calculated?
Using Naegele's rule: 280 days (40 weeks) after the first day of your last menstrual period, assuming a typical 28-day cycle.
How accurate is a due date estimate?
Only about 5% of babies are born on their exact estimated due date — most arrive within a couple of weeks either side. An early ultrasound generally gives a more accurate estimate than menstrual dating alone.
What if my cycle isn't 28 days?
Naegele's rule assumes a 28-day cycle; if yours is longer or shorter, your actual due date may differ — your healthcare provider can adjust for this or use ultrasound dating instead.
Related calculators
Sources
- Methods for Estimating the Due Date — American College of Obstetricians and Gynecologists (ACOG). Effective 01-05-2017, reviewed 13-09-2026.
This calculator provides a general estimate only and does not constitute personalized medical advice. Always confirm dates with a qualified healthcare provider.
Report a calculation issue