Pregnancy calculator
How many weeks pregnant you are, your due date and key milestones.
About this calculator
How far along am I? This pregnancy calculator tells you how many weeks and days pregnant you are, which trimester you're in and your estimated due date.
Start from the first day of your last period, a known conception date or a due date from your midwife or doctor, and see the dates of key milestones.
How it works
Pregnancy is counted from the first day of the last period, so a due date is 280 days (40 weeks) after it. A conception date is about 14 days after that day, and a known due date is counted back.
Last reviewed:
Common questions
How are pregnancy weeks counted?
From the first day of your last period, about two weeks before conception. So at conception you are already counted as about 2 weeks pregnant.
When does each trimester start?
The first trimester runs to the end of week 13, the second from week 14 to the end of week 27, and the third from week 28 until birth.
How accurate is my due date?
Only about 1 in 20 babies arrive on their due date. Most come within two weeks either side. An early ultrasound scan gives the most accurate dating.
Sources and further reading
The story behind it
Where the idea came from: Naegele's rule for due dates is named after the German obstetrician Franz Naegele, who lived from 1778 to 1851.
Naegele's rule adds about nine months and seven days to the first day of the last period, and doctors still use it as a starting point. Today an early scan often refines the date. This calculator uses the same 280-day count and turns it into weeks, trimesters and milestones.
Why you can trust this calculator
- It runs in your browser. Nothing you type into it is sent anywhere.
- The method is explained on this page, so you can check it yourself.
- Free to use, with no sign-up.
- Results are estimates, not medical advice.
- Spotted a mistake? Tell us and we'll look into it.
After 15 years as a mathematics educator, I built CalculStore to give students, teachers, professionals and anyone working with numbers simple, reliable tools.
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