CalcVitalsHow Many Weeks Pregnant Am I?
Pregnancy age is counted from the first day of your last period, not from conception. So if your last period started exactly 12 weeks ago today, you are 12 weeks 0 days pregnant — even though conception was about 10 weeks ago. Enter your date and this page counts it precisely.
How it works
The counting convention surprises almost everyone the first time: you are called two weeks pregnant at conception, and four weeks on the day of the missed period. The system dates from the last period because that is a date most people can identify, while conception usually is not — and two centuries of obstetric practice are filed under this convention, so it is not changing.
Weeks-and-days (written like 24w3d) is the unit everything in pregnancy care runs on: screening windows, scan timing, viability milestones and the definition of full term (39–40 weeks) and post-term (past 42). Knowing your exact count also makes the flood of week-by-week information usable — development descriptions are written against this same clock.
If your count from this page disagrees with a scan, believe the scan, particularly an early one: embryos grow at remarkably uniform rates in the first trimester, which is exactly why early ultrasound is the gold standard for dating. Later scans measure size, which varies naturally, and are not used to re-date.
The method
Gestational age = days from LMP to the reference date, expressed as weeks + remaining days. Due date = LMP + 280 days. Trimesters: weeks 0–13 first, 14–27 second, 28+ third.
Frequently asked questions
Why am I '2 weeks pregnant' at conception?
Because the count starts at the last period, about two weeks before ovulation. It is a dating convention, chosen because the period's start is observable and conception usually is not.
My scan says a different week than this page. Which is right?
The scan — especially before 13 weeks, when embryo growth is very uniform. Care teams will usually redates the pregnancy to the scan and use that figure from then on.
When am I full term?
Definitions refined by ACOG: early term 37–38 weeks, full term 39–40 weeks, late term 41, post-term 42 and beyond. The best outcomes cluster at 39–40.