Pregnancy Due Date Calculator — gestational age and milestones

Estimated due date

2027-06-02

10w 0d today · 210 to go days

Gestational age: 10w 0d
Trimester: First
Days: 210 to go

First day of your last period

Cycle length

28 days is the assumption

Trimesters

First trimesternow2026-08-26 → 2026-12-01

Second trimester2026-12-02 → 2027-03-09

Third trimester2027-03-10 → 2027-06-02

Milestones

14wEnd of the first trimester — the risk of miscarriage falls sharply from here2026-12-02

18wAnatomy scan window opens — usually done between 18 and 22 weeks2026-12-30

22wAnatomy scan window closes — the detailed scan is normally done by now2027-01-27

24wViability — survival outside the womb becomes possible with intensive care2027-02-10

28wThird trimester begins2027-03-10

37wFull term begins — birth from here is not considered premature2027-05-12

40wDue date — most births are not on this day2027-06-02

42wPost-term — past this, induction is usually discussed2027-06-16

Calculation

Last menstrual period2026-08-26
Counted from280 days from 2026-08-26
Estimated due date2027-06-02
Gestational age today10w 0d on 2026-11-0410
Days to go210
An estimate. Only about one birth in twenty happens on the due date, and a first-trimester scan is more accurate than any date-based method.

How to use

What it's for

Estimate a baby's due date from a date you know, and see how far along the pregnancy is today. It is general reference; the date your doctor or midwife gives is the one to follow.

Before you start

Have one date: the first day of your last period, the date of conception, an IVF transfer date, or the date of an ultrasound with the age the scan measured.

Choose what you know
Press Last period, Conception, IVF day 5, IVF day 3 or Ultrasound — whichever you have a date for.
Pick the date
Choose the date in the box that appears; its label follows your choice, such as First day of your last period or Date of the scan. For a period, use the day it started.
Set your cycle length, for Last period
With Last period, type your usual cycle in Cycle length: the days from one period's start to the next. If unsure, leave it — 28 days is the assumption.
Enter the scan result, for Ultrasound
With Ultrasound, type the age the scan measured: the whole weeks in Weeks at scan and the extra days in Days.
Press Calculate
Press Calculate. The answer already updates as you choose; the button brings it into view.

Reading the result

Estimated due date: the day the pregnancy reaches 40 weeks, with how far along you are and the days left under it. Few babies arrive on the day itself.
Gestational age: how far along the pregnancy is today, in weeks (w) and days (d). It is counted from the first day of the last period, so it is about two weeks more than the time since conception.
Trimester and Days: which third of the pregnancy you are in now, and the days left.
Trimesters and Milestones: when each trimester starts and ends, and points along the way such as Full term begins. Past ones are dimmed.

If it goes wrong

The page says that date has not happened yet: the date you picked is in the future. Check the year in the date box.
An error about Cycle length: type a whole number of days. If your cycle is outside the range the message gives, ask your doctor.
Your doctor's due date is different: an early ultrasound is more accurate than any estimate from a date, so follow theirs.

What this is

Four ways in, depending on what you know: the first day of your last period, a conception date, an IVF transfer, or a gestational age measured at a scan. All four are converted to the same anchor — the implied last period — so the due date, the trimesters and every milestone come off one number rather than four.

The last-period method adjusts for cycle length, which most calculators skip. Nothing you enter here is sent anywhere; the whole thing runs in your browser.

Questions

Why does it say I am two weeks pregnant on the day I conceived?

Because gestational age is counted from the first day of your last period, not from conception — that is the convention every clinic and every scan uses. Conception happens roughly two weeks into that count. A tool that counted from conception would report an age two weeks behind everything your doctor tells you.

Does my cycle length matter?

Yes, and most calculators ignore it. Naegele’s rule assumes a 28-day cycle with ovulation on day 14. If your cycle runs 35 days you ovulate about a week later, so the due date moves about a week later too. That week matters when the date is being used to decide whether labour is early or late.

Which method is most accurate?

An IVF transfer date, because the embryo’s age is known exactly. After that, a first-trimester ultrasound — which in practice overrides a date-based estimate when the two disagree. Conception and last-period dates are the least precise, because both rest on assumptions about when ovulation happened.

Will the baby arrive on the due date?

Almost certainly not. Only about one birth in twenty happens on the estimated date. Anything from 37 to 42 weeks is normal, which is why the tool shows the full-term window and the post-term point rather than a single day.

Is anything I type here sent anywhere?

No. Every calculation runs in your browser and there is no endpoint that would accept these dates. Nothing is stored, and closing the tab is all it takes to be rid of it.

The maths

Naegele’s rule

last period 280 days

shifted by however far your cycle differs from 28 days.

The four methods

From last period +280 days

From conception +266 days

From a day-3 transfer +263 days

From a day-5 transfer +261 days

Each offset is 280 minus how far along the pregnancy already was on that date. A day-5 blastocyst is two days older than a day-3 embryo, so the same transfer date is two days further along.