How is gestational age counted?

Gestational age is counted from the first day of the last menstrual period (LMP), not from conception. At the time of conception you are already considered about 2 weeks pregnant.

What are the pregnancy trimesters by week?

First trimester: weeks 1–12. Second trimester: weeks 13–26. Third trimester: weeks 27–40.

Pregnancy Week Calculator

Find out how many weeks pregnant you are from the first day of your last menstrual period.

Embed this tool on your site

<iframe src="https://abracalc.com/calculator/pregnancy-week-calculator/embed.html" width="340" height="320" style="border:1px solid #e4e7ec;border-radius:12px" loading="lazy"></iframe>

How to use this tool

Enter first day of last period and today's date in the fields above.
Results update instantly as you type — or click Calculate.
Read your weeks pregnant and the full breakdown beneath it.

Enter your last menstrual period date and today's date to see exactly how many weeks and days pregnant you are.

Frequently asked questions

How is gestational age counted?: Gestational age is counted from the first day of the last menstrual period (LMP), not from conception. At the time of conception you are already considered about 2 weeks pregnant.
What are the pregnancy trimesters by week?: First trimester: weeks 1–12. Second trimester: weeks 13–26. Third trimester: weeks 27–40.

References & sources

Wikipedia: Gestational age