Trimester Calculator
Enter how many weeks pregnant you are and see your trimester, how far into it you are, and how long until the next one begins.
How it works
First trimester = weeks 1–13, second = weeks 14–27, third = weeks 28–40, all counted from the first day of the last period.
Pregnancy is divided into three trimesters of roughly thirteen weeks each, counted in gestational weeks from the last menstrual period. The exact first-to-second cutoff varies between sources — anywhere from week 12 to 14 — and this tool uses the common split of weeks 1–13, 14–27 and 28–40. The small differences do not change your care, which your provider guides by your specific dates.
Worked example
At 20 weeks 0 days you are in the second trimester (weeks 14–27), six weeks into it, with the third trimester beginning in eight weeks at week 28.
Frequently asked questions
When does the second trimester start?
Most commonly at week 14 and running through week 27. Some sources start it at week 13 or 12, but week 14 is the widely used mark.
Which trimester is considered the easiest?
Many people find the second trimester the most comfortable — early nausea and fatigue often ease and the bump is not yet large. Everyone is different, though; discuss symptoms with your provider.
Do trimesters have exact boundaries?
Not universally. The differences between definitions are a week or so and do not affect medical care, which is scheduled by your exact gestational age rather than by trimester alone.
Related calculators
Educational estimates from standard formulas and population averages — every pregnancy and baby is different. This is not medical advice; your doctor, midwife or pediatrician, with an examination or ultrasound, gives the accurate guidance.