Pregnancy Week Calculator
Find how many weeks pregnant you are, your trimester and days until the due date.
About the Pregnancy Week Calculator
Enter your due date or the first day of your last period, and the date you want to check (today by default). The calculator shows how many weeks and days pregnant you are on that date, the trimester, the month of pregnancy and the days left to the due date.
Gestational age is counted from the first day of the last period, about two weeks before conception. ACOG defines the first trimester as up to 13 weeks 6 days, the second as 14 weeks 0 days to 27 weeks 6 days, and the third from 28 weeks to birth.
The formula
Gestational age = date − LMP (or date − (due date − 280 days))
Worked example
Due date 1 March 2027, checked on 11 November 2026
- LMP = 1 March 2027 − 280 days = 25 May 2026
- 11 November 2026 − 25 May 2026 = 170 days = 24 weeks 2 days
- Second trimester, 110 days to go
Things to keep in mind
- If an early scan changed your due date, use the scan date: it is more accurate than a period date.
Questions people ask
Why does pregnancy count from my period?
It's the date most people know; conception usually happens about 2 weeks later.
Is 40 weeks nine months?
About nine calendar months plus one week.
What does 24+2 mean?
24 weeks and 2 days, the way maternity notes usually write gestational age.