What happens in each trimester?

First trimester (weeks 1–12): rapid cell division, organ formation, and the highest risk of miscarriage. Second trimester (weeks 13–26): growth and movement begin, typically the most comfortable period. Third trimester (weeks 27–40): rapid growth, preparation for birth, increasing discomfort.

When does the second trimester start?

The second trimester begins at 13 weeks and 0 days of gestational age (counted from your LMP). Many people find this trimester more comfortable as early pregnancy symptoms often ease.

What is a full-term pregnancy?

A full-term pregnancy is defined as 39 weeks 0 days to 40 weeks 6 days. Early term is 37–38 weeks, late term is 41 weeks, and post-term is 42 weeks or more.

Is my data sent to a server?

All calculations run locally in your browser using JavaScript. Our servers are not involved at any point.

Pregnancy trimester calculator

Find out which trimester of pregnancy you are in right now. Enter your last menstrual period date or conception date to see your current trimester, gestational age in weeks and days, and your estimated due date. All calculations run locally in your browser. This is an estimate. Confirm with a healthcare provider.

Calculate from

First day of last period

How it works

Naegele's rule adds 280 days (40 weeks) to the first day of the last menstrual period to estimate the due date. When calculating from a conception date, 266 days are added instead (accounting for the two-week gap between LMP and ovulation). All date arithmetic runs in JavaScript using the browser's built-in Date API. Our servers are not involved.

Processing runs in your browser

All calculations happen locally in your browser tab. Our servers are not involved at any point.

This tool provides an estimate only. Confirm your due date and gestational age with a qualified healthcare provider. Ultrasound measurements may result in a different estimate.

Related operations

To find an exact age from a past birthday, try the age calculator. For working out gaps between any two dates, use the date calculator. To plan energy needs through pregnancy, see the calorie calculator.

Frequently asked questions

What happens in each trimester?: First trimester (weeks 1–12): rapid cell division, organ formation, and the highest risk of miscarriage. Second trimester (weeks 13–26): growth and movement begin, typically the most comfortable period. Third trimester (weeks 27–40): rapid growth, preparation for birth, increasing discomfort.
When does the second trimester start?: The second trimester begins at 13 weeks and 0 days of gestational age (counted from your LMP). Many people find this trimester more comfortable as early pregnancy symptoms often ease.
What is a full-term pregnancy?: A full-term pregnancy is defined as 39 weeks 0 days to 40 weeks 6 days. Early term is 37–38 weeks, late term is 41 weeks, and post-term is 42 weeks or more.
Is my data sent to a server?: All calculations run locally in your browser using JavaScript. Our servers are not involved at any point.

Last reviewed May 26, 2026

Pregnancy trimester calculator

How it works

Processing runs in your browser

Related operations

Frequently asked questions

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