Estimate Your Pregnancy Due Date

A free due date calculator that estimates when a baby is due. Enter the first day of your last period, or the conception date, and it returns the estimated due date, your current gestational age in weeks and days, the trimester and the days left to go.

How to estimate a due date

Pick a starting point

Choose to calculate from your last period or from conception.

Enter the date

Type the relevant date, and your cycle length if using the last period.

Read the estimate

The calculator shows the due date, gestational age and trimester.

Find your estimated due date and how far along you are

An estimate, not a medical date

This calculator uses Naegele's rule — a textbook formula based on a 28-day cycle. Real pregnancies vary by 1–2 weeks in either direction. An early-pregnancy ultrasound (8–13 weeks) is the most reliable way to date a pregnancy. For prenatal care, follow-up appointments and any concerns — please see an obstetrician, midwife or family doctor.

First day of last period

Cycle length

Your average cycle length — the standard 28 days is assumed if unsure.

Estimated due date

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Gestational age

—

Trimester

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Conception (est.)

Estimate only. Naegele's rule adds 280 days to your last period; only about 1 birth in 20 happens on the exact date and most arrive within a two-week window. This is not medical advice — an obstetrician, midwife or family doctor confirms the date with an ultrasound and provides prenatal care.

Features

Two ways to start Gestational age Cycle-length adjustment Trimester and days to go

Frequently Asked Questions

How is a due date calculated?

The common method is Naegele's rule: add 280 days, or 40 weeks, to the first day of the last menstrual period. From a conception date, the due date is about 266 days later.

How accurate is the due date?

It is an estimate. Only around 5% of babies arrive on the exact date; most births happen within two weeks either side. An early-pregnancy ultrasound gives the most reliable date.

What if my cycle is not 28 days?

Naegele's rule assumes a 28-day cycle with ovulation around day 14. If your cycle is longer or shorter, enter its length and the calculator shifts the estimate accordingly.

What is gestational age?

Gestational age is how far along the pregnancy is, counted in weeks and days from the first day of the last period — so it usually starts about two weeks before conception.

When should I see a doctor or midwife?

Book your first prenatal appointment as soon as you have a positive pregnancy test — most clinicians like to see you between weeks 8 and 12. Earlier if you have bleeding, severe pain, a history of miscarriage, or any chronic condition. The doctor or midwife will confirm the due date with an ultrasound, screen for risks and schedule the rest of your prenatal care. This calculator is a planning tool, not a substitute for that care.

When is the ultrasound dating most accurate?

A first-trimester ultrasound between 8 and 13 weeks gives the most reliable due date — accurate to within about 5 days. After 20 weeks the calculator estimate and the ultrasound estimate may diverge by a week or more, and clinicians keep the earlier-trimester date.

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Who is this tool for?

🏥 Healthcare Professionals 👨‍👩‍👧 Parents & Families

Published 18 May 2026 Updated 23 May 2026