Pregnancy Week Calculator

Gestational age is counted from the first day of your last menstrual period, not from conception, so you begin at week 0. The calculator takes the days between that date and the as-of date, then splits them into completed weeks plus the leftover days.

The first trimester runs from week 0 to the end of week 12, the second from week 13 to the end of week 26, and the third from week 27 until birth. The calculator labels your current trimester from your completed weeks.

It uses Naegele's rule: the estimated due date is 280 days (40 weeks) after the first day of your last menstrual period. Days remaining is simply the number of days from your as-of date to that due date.

It is an estimate, not a diagnosis. It assumes a regular 28-day cycle, and only about 1 in 20 babies arrive on the exact due date. An early ultrasound dating scan is usually more precise, so please see your doctor or midwife to confirm.

Yes. The calculation runs entirely in your browser. The dates you enter are never uploaded, logged or stored anywhere.

Your gestational age changes every day. Leaving the as-of date on today shows how far along you are right now, but you can set any date to see where you were, or will be, on that day.