What is the Pregnancy Trimester Calculator?
The Pregnancy Trimester Calculator identifies the trimester for a selected date from the LMP and shows the calendar dates when the second and third trimesters begin, along with the estimated 40-week due date.
How does the Pregnancy Trimester Calculator work?
ACOG groups pregnancy into the first trimester through 13 weeks 6 days, the second trimester from 14 weeks 0 days through 27 weeks 6 days, and the third trimester from 28 weeks 0 days onward. The calculator converts these week boundaries into calendar dates.
What formula or rule does it use?
First trimester: 0–13w6d; second: 14w0d–27w6d; third: 28w0d onward. The dynamic “How this answer was calculated” panel substitutes your entered values into that rule after a valid calculation.
How should you use this calculator?
Enter the first day of the LMP and choose the date you want to classify. If your prenatal care uses a revised EDD instead of the LMP estimate, the Pregnancy Week Calculator is a better way to map an established EDD to gestational timing.
How should you understand the result?
The result includes trimester plus exact gestational weeks and days. Boundary dates help show when the pregnancy moves from the first to second and second to third trimester under the standard gestational-age convention.
What are the limitations?
A trimester label is a timing category, not an assessment of fetal development or maternal health. Clinical decisions depend on the established gestational age and the full medical picture.
Who can use this calculator?
Use this tool for educational pregnancy calendar organization. For a full progress summary including days remaining and conception estimate, see the Pregnancy Calculator. You can estimate the EDD directly with the Due Date Calculator and review estimated conception timing with the Conception Date Calculator.
Frequently asked questions about Pregnancy Trimester
Sources and methodology
Methodology and interpretation are grounded in the following professional or government references.