Calculator Pregnancy
Pregnancy week calculator
How far along are you? Enter one date to see how many weeks and days pregnant you are today, your trimester, your estimated due date, and how much of the 40 weeks is behind you.
You are
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By the numbers Context
How “how far along” is counted
Pregnancy is dated in gestational age — the number of completed weeks and days since the first day of your last menstrual period. It sounds odd, because it means the count starts about two weeks before you actually conceived, but it is the standard every clinician uses, and it is why a full-term pregnancy is described as 40 weeks even though a baby develops for around 38. This calculator works out your current week and day from your last period, conception date, or due date.
Those 40 weeks are grouped into three trimesters: the first runs to the end of week 12, the second from weeks 13 to 27, and the third from week 28 to birth. The dates a calculator gives are estimates — only about 1 in 20 babies arrive on the exact due date — and a first-trimester ultrasound, which measures the baby directly, is the accurate reference your care team will rely on.
40 weeks
a full-term pregnancy, counted from your last period
ACOG
280 days
from the last period to the estimated due date
Naegele’s rule
~1 in 20
babies born on their exact due date
Research
Sources: American College of Obstetricians and Gynecologists (ACOG); standard obstetric dating (Naegele’s rule).
Frequently asked questions
How do I know how many weeks pregnant I am?
Count from the first day of your last menstrual period to today — that number of weeks and days is your gestational age. This calculator does it for you from your last period, conception date, or due date. A dating ultrasound gives the most accurate figure.
Is a pregnancy 39 or 40 weeks?
Full term is counted as 40 weeks from the first day of your last period, which is the due date. Babies born any time from 39 to 41 weeks are considered full term, and only about 5% arrive on the exact due date.
Does being 4 weeks pregnant mean I conceived 4 weeks ago?
No. Because pregnancy is counted from your last period — about two weeks before conception — being "4 weeks pregnant" means you conceived roughly two weeks ago, not four.
What trimester am I in?
The first trimester runs through week 12, the second from weeks 13 to 27, and the third from week 28 until birth. This calculator shows which trimester your current week falls in.
How accurate is a pregnancy week calculator?
It is a reliable estimate when your last period date is known and your cycles are regular. If your cycles are irregular or the date is uncertain, a first-trimester ultrasound is more accurate, and your clinician’s dating takes priority.