How to work out how many weeks pregnant you are
- Choose what you know: your Last period, the Conception date or your Due date from a scan.
- Pick the date. With a last period date, set your usual Cycle length if it isn’t 28 days.
- Read how many weeks and days pregnant you are today, your trimester, the days to go and the week-by-week calendar.
How the weeks are counted
Pregnancy is dated from the first day of your last period, called gestational age. A typical pregnancy lasts 40 weeks, or 280 days, from that date. If your last period started on 1 July 2026, then on 12 October 2026 you are 103 days along, which is 14 weeks 5 days, and your estimated due date is 7 April 2027.
With a conception date, the calculator counts back 14 days to the equivalent period date. With a due date, it counts back 280 days. Either way the weeks shown match what your midwife or doctor would use.
Milestones by week
| Weeks pregnant | What it marks |
|---|---|
| 14 weeks | Start of the second trimester |
| 28 weeks | Start of the third trimester |
| 37 weeks | Full term begins |
| 40 weeks | Estimated due date |
The week-by-week table under the result lists the date each week starts, so you can see on which day you reach each milestone. Your dates stay in your browser and aren’t sent anywhere.