Pregnancy Due Date Calculator

Q: 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 usually gives the most accurate estimate.

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

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

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.

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