Pregnancy Due Date Calculator
Estimate your due date and current week of pregnancy from your last menstrual period.
Pick the first day of your last menstrual period.
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How Due Dates Are Calculated
The most common method is Naegele's rule: due date = first day of LMP + 280 days (40 weeks). Pregnancy is divided into three trimesters by gestational week.
Trimesters by Gestational Week
| Trimester | Weeks |
|---|---|
| First trimester | 0 – 12 weeks |
| Second trimester | 13 – 26 weeks |
| Third trimester | 27 – 40 weeks |
Results are estimates for reference only and are not medical advice. A dating ultrasound and your doctor or midwife give the most accurate dating.
Frequently Asked Questions
- How is the due date calculated?
- By Naegele’s rule: the estimated due date is the first day of your last menstrual period (LMP) plus 280 days (40 weeks). Equivalently, take the LMP, subtract 3 months and add 7 days.
- How accurate is the estimated due date?
- It is an estimate. Only about 4% of babies are born on their exact due date, and most arrive within two weeks either side of it. A dating ultrasound in the first trimester can refine the date.
- What is gestational age?
- Gestational age counts weeks from the first day of your LMP, not from conception. So at "8 weeks pregnant" you are 8 weeks from your LMP, roughly 6 weeks from conception.
- My cycle is irregular — is this still accurate?
- LMP-based dating is less reliable with irregular or long cycles. Your doctor or midwife may adjust the due date based on a dating ultrasound.
📅 Last updated: June 2026 · Formulas follow standard banking / tax conventions · Results are for reference only.