Pregnancy Due Date Calculator

Estimated due date: 25 May 2027
How far along: 10 weeks, 0 days
Trimester: First (up to 12 weeks)
Days to the due date: 210 days
Likely conception date: 1 September 2026

What it does

Estimate your baby's due date and how many weeks pregnant you are. Work it out from the first day of your last period, a known conception date, an IVF transfer date or a dating scan. You also see your trimester, the days left to go and the likely conception date.

How to use it

Work it out from: Most people use the first day of their last period. If you've had a dating scan, use that: it's what your midwife goes by.
First day of your last period: The day your last period started, not the day it ended.
Usual cycle length: Days from the start of one period to the start of the next. 28 is average; a longer cycle usually means a later due date.
Date of conception: Only if you know it, for example from ovulation tracking.
Embryo transfer date: The day the embryo was transferred. Choose 3-day or 5-day (blastocyst) above.
Date of the scan: The day of your dating scan, usually at 10 to 14 weeks.
Weeks at the scan: How many weeks pregnant the scan said you were: for 12 weeks and 3 days, enter 12 here and 3 below.
Plus days: The extra days, from 0 to 6.
How far along on: The date to show how many weeks pregnant you are on. It starts as today.

Common uses

Planning maternity leave and telling your employer in time.
Knowing which week of pregnancy you're in.
Counting down the days. Try the Days Between Dates Calculator
Checking your weight before pregnancy. Try the BMI Calculator

The formula

From your last period: due date = first day of last period + 280 daysCycle not 28 days: add (cycle length − 28) daysFrom conception: due date = conception + 266 daysIVF: 3-day transfer + 263 days, or 5-day transfer + 261 daysWeeks pregnant = days since the first day of the last period ÷ 7

Where:

280 days: 40 weeks: pregnancy is counted from the first day of the last period, about 2 weeks before conception

This is Naegele's rule, the standard method. A dating scan is more accurate, and your midwife will confirm your due date from it.

Worked example

With a last period starting on 1 January 2026 and a cycle of 28 days:

Due date: 1 January 2026 + 280 days = 8 October 2026
On 12 March 2026, that's 10 weeks, 0 days pregnant
Trimester: First (up to 12 weeks)
Likely conception: about 15 January 2026

Questions people ask

How accurate is a due date?

It's an estimate. Only around 1 in 20 babies arrive on their due date, and most are born within a week or two either side. A pregnancy is full term from 37 weeks.

Why am I 2 weeks pregnant before I conceived?

Pregnancy is counted from the first day of your last period, because that date is usually known and conception isn't. Conception typically happens about 2 weeks later, so at conception you're already counted as 2 weeks pregnant.

What if my scan gives a different date?

Go by the scan. A dating scan at 10 to 14 weeks measures the baby directly, so it's more reliable than counting from a period, especially if your cycles are irregular. In the UK, the NHS offers one to everyone.

Last checked 26 October 2026