Pregnancy Week Calculator
Find out how many weeks and days pregnant you are from your last period — with your trimester, days remaining and progress to 40 weeks.
How it works
gestational age = today − first day of last period, in weeks and days · full term = 40 weeks (280 days) · progress = days ÷ 280
Gestational age is counted from the first day of your last period, so at conception you are already about two weeks along and at 4 weeks pregnant conception was only about two weeks ago — this is the standard clinicians use. Full term is 40 weeks, though babies are considered “early term” from 37 weeks and commonly arrive a couple of weeks either side of the due date. The count uses today’s date; if an ultrasound revised your dates, use your provider’s numbers instead.
Worked example
A last period on June 1, 2026, viewed on September 11, 2026: 102 days have passed — 14 weeks 3 days, in the second trimester, about 36% of the way to a March 8, 2027 due date, with 178 days to go.
Frequently asked questions
Why am I “pregnant” before I conceived?
Gestational age is counted from the first day of your last period, roughly two weeks before you ovulate and conceive. It’s the convention used on ultrasounds and in maternity care, so everyone works from the same clock.
When is a baby considered full term?
40 weeks is the due-date mark, but 37–38 weeks is “early term” and 39–40 weeks is “full term.” Arriving within a couple of weeks either side is common; your provider monitors this.
Does this match my ultrasound dating?
It may differ by a few days to a week. Early ultrasound measurements can be more accurate than the last-period date, so if your provider revised your dates, follow theirs.
Related calculators
Estimates based on standard formulas and average cycles — every pregnancy is different. This is not medical advice; your doctor or midwife, with an ultrasound, gives the accurate dates and guidance.