Gestational age is measured from the first day of the last menstrual period (LMP). Total pregnancy is conventionally 40 weeks (280 days): trimester 1 = weeks 1–12, trimester 2 = 13–26, trimester 3 = 27–40.
Current gestational age
0 wk 0 d
Trimester
—
Days completed
0 / 280
% complete
0%
Estimated due date
—
Days remaining
0
How weeks are counted
Week 1 is technically the week of your LMP — you weren’t actually pregnant yet (ovulation/conception is roughly week 2–3).
An ultrasound dating scan in the first trimester is more accurate if your cycles are irregular or you don’t know your LMP exactly.
"Term" births are 37–42 weeks; only about 4% of babies arrive on the exact due date.