How accurate is a due date?

A due date is an estimate, not a deadline. Only about 1 in 20 babies are born on their exact due date, and a healthy full-term birth can happen any time between 37 and 42 weeks. First-trimester dating ultrasounds and IVF dates are the most accurate; the last-period method is less precise if your cycles are irregular.

Can I calculate my due date from the conception or IVF date?

Yes. If you know your conception or ovulation date, the calculator adds 266 days. For IVF, it counts forward from the transfer: 263 days for a day-3 embryo and 261 days for a day-5 blastocyst, since the embryo's age is already known.

How far along am I right now?

Pregnancy is measured in weeks and days from the first day of your last period. Once you enter your date, this calculator shows how many weeks and days along you are, which trimester you're in, and how many weeks you have left until your due date.

when's the big day?

Pregnancy due date calculator

Find your estimated due date and exactly how far along you are. Calculate from your last period, the conception date, or an IVF transfer — it only takes a few seconds.

Calculate from

First day of your last period

Average cycle length (days)

Your due date appears here

Pick a method and fill in the date above to see your estimated due date and how far along you are.

This is an estimate, not medical advice. Only about 1 in 20 babies arrive on their exact due date — always confirm your dates with your midwife or doctor.

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Let everyone guess this date

You've got a due date — now turn it into a game. Create a free baby pool and let friends and family guess the exact day your little one arrives. Closest guess wins.

Create a free baby pool

Set up in about a minute — share one link with everyone.

the maths, briefly

How your due date is worked out

From your last period

The classic method (Naegele's rule) adds 280 days — 40 weeks — to the first day of your last menstrual period. If your cycle is longer or shorter than the average 28 days, we adjust the estimate by the difference, because ovulation shifts with your cycle.

From conception or ovulation

If you know the day you conceived or ovulated, we add 266 days (38 weeks). Pregnancy is dated from the last period rather than conception, which is why this is two weeks shorter than the last-period method.

From an IVF transfer

IVF gives the most precise dating because the embryo's age is known. We count forward from a known point: a day-3 embryo is due 263 days after transfer, and a day-5 blastocyst 261 days after transfer.

Quick answers

Due date questions

The standard method adds 280 days (40 weeks) to the first day of your last menstrual period, assuming a 28-day cycle. This calculator adjusts for your actual cycle length, and can also work from a conception date (+266 days) or an IVF transfer date (+263 days for a day-3 embryo, +261 for a day-5 blastocyst).

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Make the wait more fun

Baby due date pool

Turn your due date into a game — everyone guesses the day baby actually arrives.

What is a baby pool?

New to baby pools? The complete guide to how they work and how to set one up.