How does the Pregnancy Calculator work?

Identify the first day of your last menstrual period (LMP) Then: Add 280 days (40 weeks) to get the estimated due date (Naegele's Rule) Then: Calculate gestational age: today − LMP in weeks and days Then: Determine trimester: weeks 1–12 (first), 13–26 (second), 27–40 (third).

Can you give an example of how to use the Pregnancy Calculator?

Example: Input LMP: January 1 gives a result of Due date: October 8 (Add 280 days to LMP).

Is the Pregnancy Calculator free to use?

Yes — completely free with no registration, download, or subscription required. All calculations happen instantly in your browser.

How accurate is the Pregnancy Calculator?

Our Pregnancy Calculator uses verified mathematical formulas and is accurate to multiple decimal places. Results are calculated in real-time using the same methods used by professionals.

Practic

Pregnancy Calculator

First day of last period

A pregnancy calculator estimates your due date, current gestational age, and trimester based on your last menstrual period (LMP) or conception date. Pregnancy lasts approximately 40 weeks (280 days) from the LMP, though normal term is considered 37–42 weeks.

Trimester	Weeks	Key Development
First	1–12	Major organs form; miscarriage risk highest
Second	13–26	Movement felt; anatomy scan at week 20
Third	27–40	Rapid growth; lung maturation; birth
Full term	37–40	Baby ready for birth
Post-term	42+	Induction often recommended

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Pro Tip

The first trimester is the most critical for fetal development. Folic acid supplementation (400–800 mcg/day) before and during early pregnancy significantly reduces neural tube defect risk.

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Did You Know?

Only about 4% of babies are born exactly on their due date. Most births occur within 2 weeks before or after.

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Pregnancy Calculator

Pregnancy Calculator

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