Pregnancy Due Date Calculator

Estimate your baby’s due date and current week of pregnancy.

Calculate By

First Day of Last Menstrual Period

Estimated Due Date–

Current Gestational Age–

Current Trimester–

Days Remaining–

Based on Naegele’s Rule (280 days / 40 weeks from LMP, or 266 days from conception). Only about 5% of babies are born exactly on their due date — this is an estimate. Always confirm with your doctor or an ultrasound dating scan.

How Due Dates Are Calculated

From Last Menstrual Period (LMP)
Due date = LMP date + 280 days (40 weeks). This is the standard method used by most doctors (Naegele’s Rule), since ovulation and conception are hard to pinpoint exactly.

From Conception Date
Due date = Conception date + 266 days (38 weeks). Use this if you know your exact ovulation or conception date, e.g. from fertility tracking or IVF.

Trimester 1
Weeks 1 to 12 — early development, morning sickness is common.

Trimester 2 & 3
Weeks 13–26 (2nd) and weeks 27–40+ (3rd) — most people feel their most energetic in the 2nd trimester.

Frequently Asked Questions

How accurate is a due date calculator?

It’s an estimate, not a guarantee — only about 5% of babies are born on their exact due date. Most babies arrive within 1-2 weeks before or after. An early ultrasound (8-12 weeks) usually gives the most accurate estimate.

Why is pregnancy counted as 40 weeks from LMP if conception happens later?

Medical convention counts pregnancy from the first day of your last menstrual period, not from conception, because the LMP date is usually known precisely while the exact conception/ovulation date usually is not.

Also try our BMI Calculator or BMR & Calorie Calculator.

What this calculator estimates

A due date is an estimate of 40 weeks from the first day of the last menstrual period, or an equivalent estimate from conception or ultrasound dating.

Worked examples

If the last menstrual period began on January 1, the estimated due date is around October 8.
If conception is estimated as January 15, adding about 266 days gives an estimated due date around October 8.

Methodology and assumptions

Last-menstrual-period dating adds 280 days to the first day of the LMP; conception-based dating adds about 266 days. These rules assume reliable dates and do not incorporate ultrasound measurements, assisted-reproduction details, irregular cycles, or a clinician’s redating decision unless explicitly entered.

Authoritative sources

Methods for Estimating the Due DateAmerican College of Obstetricians and Gynecologists

Sources last checked September 10, 2026. Regulations and guidance can change; use the linked authority for the current position.

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Content maintained by Ajit Naskar. Medical review status: Not independently reviewed by a qualified clinician. Existing content is frozen against substantive expansion; sources and limitations were last audited on September 10, 2026.