Pregnancy Trimester Calculator
See the start and end dates of each pregnancy trimester and which trimester you are in. Works from your last period or your due date.
Calculator by Toolsloft ↗- Current trimester
- Trimester 3
- First trimester
- 2026-01-01 to 2026-04-08
- Second trimester
- 2026-04-09 to 2026-07-15
- Third trimester
- 2026-07-16 to 2026-10-08
- Due date
- 2026-10-08
Pregnancy is split into three trimesters, and knowing the exact dates for each helps with appointments, tests, and planning. Enter the first day of your last period or your due date, and this calculator maps out all three trimesters and tells you which one today falls in.
How this is calculated
Trimesters are counted in gestational weeks from the first day of the last menstrual period (LMP). The first trimester runs from week 0 through 13 weeks 6 days, the second from 14 through 27 weeks 6 days, and the third from 28 weeks to the 40-week due date. From a due date the LMP is recovered as due minus 280 days (the Naegele rule). This is an estimate, and your provider dating may differ.
How to use
- Choose whether you are entering your last period date or your due date.
- Enter that date, then the date you want to check against (today by default).
- Read the date range for each trimester and your current trimester.
Examples
- Last period 2026-01-01:
Due 2026-10-08; trimester 2 runs Apr 9 to Jul 15 - Due date 2026-10-08, as of 2026-07-01:
Currently in the second trimester
FAQ
- How are the trimesters divided?
- First trimester: week 0 to 13 weeks 6 days. Second: 14 to 27 weeks 6 days. Third: 28 weeks to birth, typically around 40 weeks. All counted from the last period.
- What if I only know my due date?
- Choose the due date option. The calculator works backward to your last period using the standard 280-day pregnancy length, then maps the trimesters.
- Is this the same as the dating from my provider?
- It uses the standard LMP method. An early ultrasound can shift your dates by a few days, so the figures from your provider take precedence.