Pregnancy calculator
The due date, how far along you are, and the dates ahead.
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This tool runs entirely in your browser. What you paste is processed on your device and is never sent to a server, so it is safe to use with tokens, keys and unpublished text.
Example
Example: the due date from a last period on 2 March 2026
The first day of the last period was Monday 2 March 2026, with a 28-day cycle. The due date is that day plus 280 days. To show what “today” looks like, the result is read on 15 June 2026.
- Due date: Mon, 7 December 2026 (2 March + 280 days, Naegele’s rule).
- On 15 June 2026: 15 weeks (15+0), 2nd trimester, 175 days to go; estimated conception Mon, 16 March 2026.
- Key dates: end of the 1st trimester 7 Jun 2026 (13+6), halfway 20 Jul, 3rd trimester from 14 Sept, term (37 weeks) 16 Nov.
| Count from | Date | Due date |
|---|---|---|
| Last period, 28-day cycle | 2 March 2026 | Mon, 7 December 2026 |
| Last period, 32-day cycle | 2 March 2026 | Fri, 11 December 2026 |
| Last period, 25-day cycle | 2 March 2026 | Fri, 4 December 2026 |
| Conception | 16 March 2026 | Mon, 7 December 2026 (+ 266 days) |
| IVF, day-5 blastocyst | 21 March 2026 | Mon, 7 December 2026 (+ 261 days) |
| IVF, day-3 embryo | 19 March 2026 | Mon, 7 December 2026 (+ 263 days) |
When the dates agree, every route lands on the same estimated day. It is an estimate: most babies arrive within two weeks either side, and your midwife or doctor may move the date after an early scan.
How it works
- Choose what you know: the first day of your last period, the day of conception, an IVF transfer, or the due date from your scan.
- Pick the date, and with a period, your usual cycle length (28 days if you are not sure).
- The due date appears with how far along you are today, the trimester, the days to go and a list of key dates.
Frequently asked questions
- How is the due date worked out?
- By Naegele’s rule: the first day of the last period plus 280 days, 40 weeks. With a longer or shorter cycle than 28 days, the date moves by the difference, since ovulation comes later or earlier.
- Why do the weeks count from the period and not from conception?
- Because the period is the date most people know. Conception is usually about two weeks later, so at "6 weeks" the embryo is about 4 weeks old.
- What does 15+3 mean?
- 15 completed weeks and 3 days — you are in the 16th week of pregnancy.
- How exact is the due date?
- Only a few babies arrive on it: most are born within two weeks either side. An early ultrasound dates a pregnancy more precisely, and your midwife or doctor may move the date after it.
- How do I work out how many weeks pregnant I am?
- Count the days from the first day of your last period and divide by seven: from 2 March to 15 June 2026 is 105 days, exactly 15 weeks, written 15+0. The calculator does this for today’s date and adds the trimester and the days to go.
- How is the due date worked out from an IVF transfer?
- From the transfer date: a day-5 blastocyst plus 261 days, a day-3 embryo plus 263 days. A day-5 transfer on 21 March 2026 gives Mon, 7 December 2026. The date your clinic gives you takes precedence.
- Is anything uploaded?
- No. It is worked out in your browser, and nothing you type leaves your computer.
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