Pregnancy Calculator
This pregnancy calculator works out how many weeks pregnant you are from your last period or due date — with your current week, trimester, progress and estimated due date.
How “how far along” is measured
Pregnancy is dated in gestational weeks counted from the first day of your last menstrual period (LMP), which is roughly two weeks before conception actually happens. That is why you are considered about four weeks pregnant at the time of a missed period, even though the embryo is only about two weeks old. Gestational age is written as completed weeks and days, such as "12 weeks 3 days", while in everyday speech people say they are "in week 13". A full-term pregnancy is 40 weeks from the LMP, and this calculator shows both your exact gestational age and how much of those 40 weeks is complete.
The three trimesters
The first trimester covers weeks 0 to 13, the second weeks 14 to 27, and the third from week 28 until birth. Each brings different changes, appointments and scans. Knowing your current week helps you follow week-by-week guidance, prepare for antenatal visits, and understand where you are on the journey. When you know your due date instead of your last period, switch to the Due date tab and the calculator works backwards to the same result.
Frequently Asked Questions
How many weeks pregnant am I?
What is the difference between gestational age and the week I'm in?
Which trimester am I in?
Is this medical advice?
Related tools
Estimate the big day with the Due Date Calculator, or plan ahead with the Calendar & Date tools.