Third Trimester Start Calculator

About this calculator

Pregnancy is conventionally divided into three trimesters, and the third trimester is defined as beginning at 28 weeks of gestation and running through delivery, typically around 40 weeks. Because gestational age is tracked in days and weeks from the first day of the last menstrual period (or adjusted from a dating ultrasound), figuring out how far away the third trimester is just means counting the days remaining until the pregnancy reaches the 28-week mark.

Expectant parents track this milestone because the third trimester brings a shift in prenatal care — visit frequency typically increases, additional screenings are scheduled, and it's the period where fetal growth, positioning and birth preparation become the clinical focus, making it a natural planning marker separate from the raw week count.

This calculator takes how many days pregnant you currently are (or your last menstrual period date), and returns the days and weeks remaining until your third trimester begins at 28 weeks.