Pregnancy Week Calculator
Find out how many weeks and days pregnant you are — from your last period, due date, conception, IVF transfer or an ultrasound — with your pregnancy week, month, trimester, days remaining and a milestone timeline, today or on any date.
How it works
gestational age = date checked − dating start, in weeks and days · dating start = last period (+ cycle length − 28), due date − 280 days, conception − 14 days, IVF transfer − (14 + embryo age) days, or scan date − gestational age at the scan · week = completed weeks + 1 · 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 — this is the standard clinicians and ultrasound reports use. If you know your due date, conception date, IVF transfer date or an ultrasound result instead, the calculator works back to the same starting point (280 days before the due date, 14 days before conception, 17 or 19 days before a day-3 or day-5 transfer, or the scan date minus the measured age). The result is shown as completed weeks and days, the week you are in, the trimester (first through 13 weeks 6 days, second through 27 weeks 6 days, third from 28 weeks) and a month from a common nine-month chart. The count uses today unless you pick another date, so you can also see how far along you will be on a holiday or an appointment.
Worked example
A last period on June 1, 2026, checked on September 11, 2026: 102 days have passed — 14 weeks 4 days, in week 15, the second trimester and month 4. That is about 36% of the way to a March 8, 2027 due date, with 178 days to go, and the anatomy scan window (18–22 weeks) runs October 5 to November 2, 2026.
Sources: ACOG Committee Opinion 700 — Methods for Estimating the Due Date · ACOG Committee Opinion 579 — Definition of Term Pregnancy
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.
Am I 12 weeks or in week 13?
Both describe the same day. “12 weeks 3 days pregnant” counts completed weeks; you are then in your 13th week. The calculator shows both.
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,” with late term at 41 weeks and post-term from 42. 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, choose “Ultrasound scan” or “Due date” and enter theirs.
How many months pregnant am I?
The result uses a common chart: month 1 is up to 4 weeks, month 3 ends at 13 weeks, month 6 covers 23–27 weeks and month 9 runs from 36 weeks to birth. For an exact conversion through the calendar, use the pregnancy weeks to months calculator.
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.