How are weeks of pregnancy counted?

Pregnancy weeks are counted from the first day of your last menstrual period (LMP), not from conception. Conception typically occurs around week 2. So at 4 weeks pregnant, you may have actually conceived only about 2 weeks ago.

When does each trimester start?

The first trimester is weeks 1–12. The second trimester is weeks 13–26. The third trimester begins at week 27 and continues until birth, typically around week 40.

What is gestational age vs foetal age?

Gestational age counts from the LMP and is used by healthcare providers. Foetal age (embryonic age) counts from conception and is typically about 2 weeks less than gestational age. This calculator uses gestational age, the standard medical measure.

Is my data sent to a server?

All calculations run locally in your browser. No data is sent to our servers.

Pregnancy week calculator

Find out exactly how many weeks and days pregnant you are right now. Enter your last menstrual period date or conception date and this calculator shows your gestational age in weeks and days, your current trimester, and your estimated due date. All calculations run locally in your browser. Confirm your dates 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

How are weeks of pregnancy counted?: Pregnancy weeks are counted from the first day of your last menstrual period (LMP), not from conception. Conception typically occurs around week 2. So at 4 weeks pregnant, you may have actually conceived only about 2 weeks ago.
When does each trimester start?: The first trimester is weeks 1–12. The second trimester is weeks 13–26. The third trimester begins at week 27 and continues until birth, typically around week 40.
What is gestational age vs foetal age?: Gestational age counts from the LMP and is used by healthcare providers. Foetal age (embryonic age) counts from conception and is typically about 2 weeks less than gestational age. This calculator uses gestational age, the standard medical measure.
Is my data sent to a server?: All calculations run locally in your browser. No data is sent to our servers.

Pregnancy week calculator

How it works

Processing runs in your browser

Related operations

Frequently asked questions

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