Pregnancy Trimester Calculator

About this calculator

A full-term pregnancy is conventionally divided into three trimesters based on gestational week: the first trimester runs from week 1 through week 13, the second from week 14 through week 27, and the third from week 28 until birth, typically around week 40. Gestational age is counted from the first day of the last menstrual period, not from conception, which is why it runs about two weeks ahead of fetal age.

Obstetricians and midwives use trimester boundaries to structure prenatal care — timing screening tests like the first-trimester combined screen, the anatomy scan around 18-20 weeks, and the third-trimester glucose tolerance test — and expecting parents use them as a quick way to track which developmental stage and set of symptoms to expect. Each trimester carries its own typical milestones, from early morning sickness in the first to fetal movement in the second and pre-birth preparation in the third.

This calculator takes your current week of pregnancy and tells you which trimester you’re in and how many weeks remain until the next one starts or until your due date.