Pregnancy due date calculator
Work out your estimated due date from the first day of your last period, your conception date or your IVF transfer date, and see how many weeks pregnant you are today, with the key dates ahead.
Estimated due date
This calculator gives an estimate for information only. It is not medical advice: your midwife or doctor will confirm your due date.
Key dates in your pregnancy
| Stage | Weeks | Dates |
|---|---|---|
| Dating scan window (NHS) | 11–14 | – |
| Second trimester begins | 14 | – |
| Mid-pregnancy scan window (NHS) | 18–21 | – |
| Third trimester begins | 28 | – |
| Early term | 37–38+6 | – |
| Full term | 39–40+6 | – |
| Due date | 40 | – |
| Late term | 41–41+6 | – |
| Post-term begins | 42 | – |
Milestones follow your estimated due date. Your midwife or doctor may change the due date after your first scan.
How to use it
- Choose what you know: the first day of your last period, a conception date, an IVF transfer date or a due date you already have.
- Enter the date. For your last period, change the cycle length if your cycle is usually shorter or longer than 28 days.
- Read your due date, how far along you are today and the key dates of your pregnancy.
How the due date is calculated
The standard method adds 280 days, or 40 weeks, to the first day of your last period. It assumes a 28-day cycle, so the calculator moves the date later or earlier if your cycle is longer or shorter.
From a known conception date the due date is 266 days later. For IVF, the American College of Obstetricians and Gynecologists (ACOG) counts 261 days from the transfer of a day-5 embryo and 263 days from a day-3 embryo.
How pregnancy weeks are counted
Pregnancy weeks are counted from the first day of your last period, not from conception, so you are already about two weeks pregnant when you conceive. The NHS notes that pregnancy normally lasts from 37 to 42 weeks from that date, so the due date is an estimate rather than an appointment.
Your scan may change the date
Your first ultrasound, usually offered at 11 to 14 weeks in the UK, measures the baby and gives a more accurate estimate. The due date worked out from your last period may be adjusted to match it, and from then on the scan date is the one to follow.
Early, full and late term
- Early term: 37 weeks 0 days to 38 weeks 6 days
- Full term: 39 weeks 0 days to 40 weeks 6 days
- Late term: 41 weeks 0 days to 41 weeks 6 days
- Post-term: 42 weeks 0 days and beyond
These definitions come from ACOG. They replaced the older habit of calling any birth from 37 weeks “term”, because babies born at 39 weeks or later tend to do better than those born at 37 or 38.
Due dates by last period
| Last period started | Estimated due date |
|---|---|
| 1 January 2026 | 8 October 2026 |
| 1 February 2026 | 8 November 2026 |
| 1 March 2026 | 6 December 2026 |
| 1 April 2026 | 6 January 2027 |
| 1 May 2026 | 5 February 2027 |
| 1 June 2026 | 8 March 2027 |
| 1 July 2026 | 7 April 2027 |
| 1 August 2026 | 8 May 2027 |
| 1 September 2026 | 8 June 2027 |
| 1 October 2026 | 8 July 2027 |
| 1 November 2026 | 8 August 2027 |
| 1 December 2026 | 7 September 2027 |
| 1 January 2027 | 8 October 2027 |
| 1 February 2027 | 8 November 2027 |
| 1 March 2027 | 6 December 2027 |
| 1 April 2027 | 6 January 2028 |
| 1 May 2027 | 5 February 2028 |
| 1 June 2027 | 7 March 2028 |
| 1 July 2027 | 6 April 2028 |
| 1 August 2027 | 7 May 2028 |
| 1 September 2027 | 7 June 2028 |
| 1 October 2027 | 7 July 2028 |
| 1 November 2027 | 7 August 2028 |
| 1 December 2027 | 6 September 2028 |
Frequently asked questions
How is my due date calculated?
Add 280 days (40 weeks) to the first day of your last period, adjusting for your cycle length if it isn't 28 days. From a conception date, add 266 days. Your first scan may then refine the date.
How many weeks pregnant am I?
Count the weeks from the first day of your last period. The calculator does this for you and shows the weeks and days, as well as which trimester you're in.
How accurate is a due date?
It's an estimate. Pregnancy normally lasts anywhere from 37 to 42 weeks, and a first-trimester scan gives a more accurate date than the last period alone.
What if my cycle isn't 28 days?
With a longer cycle you probably ovulated later, so the due date moves later by the same number of days; with a shorter cycle it moves earlier. Enter your usual cycle length and the calculator adjusts.
How is the due date worked out after IVF?
From the embryo transfer date: 261 days for a day-5 embryo and 263 days for a day-3 embryo, following ACOG guidance. Your clinic will confirm the date it uses.
When is a baby full term?
ACOG defines full term as 39 weeks 0 days to 40 weeks 6 days. From 37 weeks it is early term, and from 42 weeks post-term.
Sources
Also try: Ovulation calculator