Due date calculator
Your due date is 280 days (40 weeks) after the first day of your last period, adjusted for your cycle length. Enter your date below to see your due date, how many weeks pregnant you are and when your scans and tests are due.
How the due date calculator works
Doctors date pregnancy from the first day of your last menstrual period (LMP), not from the day you conceived. That's because most people know when their period started, but not exactly when they ovulated. Counting this way, a full-term pregnancy lasts about 40 weeks, even though your baby has only been growing for about 38 of them.
- From your last period: due date = first day of last period + 280 days. If your cycle is longer than 28 days, add the extra days; if it is shorter, take them away.
- From conception: due date = conception date + 266 days.
- After IVF: due date = day-5 transfer date + 261 days, or day-3 transfer date + 263 days.
Example
If your last period started on 1 January and your cycle is 28 days, your due date is 8 October. If your cycle is usually 32 days, you probably ovulated 4 days later, so your due date moves to 12 October.
| Last period started | Due date (28-day cycle) |
|---|---|
| 1 January | 8 October |
| 1 March | 6 December |
| 1 May | 5 February |
| 1 July | 7 April |
| 1 September | 8 June |
| 1 November | 8 August |
These dates assume no 29 February falls between your period and your due date. If one does, the due date is one day earlier.
What happens after you know your due date
Book your first antenatal appointment for around 8 to 10 weeks. Your dating scan, usually between 11 and 14 weeks, will check your baby's measurements and confirm or adjust your due date. The calculator above lists your key dates, including the anomaly scan at 18 to 21 weeks and the glucose test at 24 to 28 weeks. Follow your baby's growth in our pregnancy week-by-week guide.
Due date questions
How is my due date calculated?
Your due date is usually 280 days (40 weeks) after the first day of your last period. This assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, the date moves by the same number of days. This is called Naegele's rule.
How accurate is a due date calculator?
It gives a good estimate, but only about 1 in 20 babies are born on their due date. Most arrive between 37 and 42 weeks. A dating scan between 11 and 14 weeks measures your baby and is the most accurate way to confirm your due date.
Can my due date change?
Yes. If your first-trimester dating scan gives a date more than about 5 to 7 days different from your period-based date, your doctor will usually change your due date to match the scan. After that, it normally stays the same, even if later scans suggest your baby is bigger or smaller.
How do I calculate my due date after IVF?
Use your embryo transfer date. For a day-5 blastocyst transfer, your due date is 261 days after transfer. For a day-3 transfer, it is 263 days after transfer. Choose the IVF option in the calculator above.
What if I don't know the date of my last period?
Use the date you conceived if you know it, or ask your doctor for a dating scan. A scan in the first trimester can date your pregnancy accurately to within a few days.
This calculator gives an estimate for information only. Always follow the due date your doctor or midwife gives you.