Pregnancy Week Calculator

Enter the first day of your last period and a check date to see how far along you are and which trimester you are in. Estimate only, not medical advice.

Source: ACOG Committee Opinion No. 700 (2017) ↗

This result is an estimate only. Check with your bank or the relevant authority before making decisions.

How it is calculated

Days = check date − first day of last period
Weeks = days ÷ 7 (whole part), and the remainder is the extra days
First trimester: under 14 weeks; second: under 28 weeks; third: after that
Due date = first day of last period + 280 days

An error is shown if the check date is before the last period or more than 300 days after it. Estimate only, not medical advice.

Worked example

First day of last period 10 January 2026, checked on 30 September 2026:

Days = 263
263 ÷ 7 = 37 weeks and 4 days
Trimester: third
Estimated due date: 17 October 2026

Why your number may differ

The result depends on the last period date you enter, and it is only an estimate. Estimate only, not medical advice.

Frequently asked questions

How is the trimester decided?

The first trimester is under 14 weeks, the second is under 28 weeks, and after that it is the third trimester.

Why is pregnancy counted from the last period?

This calculator counts the days from the first day of your last period, then converts them into weeks and days.

Is the result accurate?

It is an estimate only. An ultrasound is more accurate. Estimate only, not medical advice.