How accurate is an LMP-based due date?

About 5% of babies are born on their estimated due date; roughly 80% arrive within ±2 weeks. Early ultrasound is more accurate, especially for irregular cycles.

What is Naegele's rule?

Add 280 days (40 weeks) to the first day of your last menstrual period. We adjust for cycle length so a 32-day cycle pushes the due date later.

When does each trimester start?

First trimester: weeks 1–12. Second: weeks 13–26. Third: weeks 27 until birth.

Is this medical advice?

No — this is an educational estimate. Confirm your due date with your healthcare provider.

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Health Calculators

Pregnancy Due Date Calculator

Estimate your due date and current week of pregnancy from your last period.

Health Calculators

First day of last menstrual period (LMP)

Average cycle length (days)

Typical range 21–35. Default 28.

Result

Estimated Due Date

Friday, July 9, 2027

Current Stage

0w 0d

First trimester

Conception (approx.)

Friday, October 16, 2026

Formula

Due date = LMP + 280 days, adjusted for cycle length

How to use the Pregnancy Due Date Calculator

Enter the first day of your last menstrual period (LMP)
Adjust the cycle length if it isn't 28 days
See estimated due date, current week and trimester

Frequently asked questions

4 answers

Pregnancy Due Date Calculator

Result

Formula

How to use the Pregnancy Due Date Calculator

Frequently asked questions

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