Pregnancy Week Calculator

Find out exactly how far along you are. Enter your last menstrual period, your due date, or the week you already know — and see your gestational age, due date, trimester, and pregnancy progress instantly.

The first day of your last menstrual period (LMP).

Your results (calculated as of today)

Current gestational age
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Estimated due date: —
You have reached 42 weeks (post-term). Please contact your prenatal care provider or go to the hospital soon.
Trimester
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Days to due date
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Estimated LMP
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Progress
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Pregnancy progress
ConceptionFull term (40 w)
First trimester
Weeks 1–13 + 6 days
Organ formation and the earliest, most delicate stage of development.
Second trimester
Weeks 14–27 + 6 days
Rapid growth, the first noticeable kicks, and the anatomy scan.
Third trimester
Weeks 28+
Final growth and maturity as your baby gets ready for birth.

This calculator uses Naegele's rule (due date = LMP + 280 days) and is for general information only. It is not medical advice — always follow your prenatal care provider's guidance.

How pregnancy weeks are calculated

Pregnancy is measured in weeks, counted from the first day of your last menstrual period (LMP) — not from the day of conception. That means during "week 1" and "week 2" of pregnancy you are not actually pregnant yet; ovulation and fertilization usually happen near the end of week 2 or the start of week 3. Counting from the LMP is the convention doctors use because it gives everyone a consistent starting point, even though it adds roughly two weeks before conception.

Your estimated due date is calculated with Naegele's rule: take the first day of your last period, add 280 days (40 weeks). This is an estimate — only about 4–5% of babies arrive exactly on their due date, and a full-term pregnancy is considered anywhere from 37 to 42 weeks.

Pregnancy is divided into three trimesters. The first trimester (weeks 1–13) is when all of the major organs form and the risk of early miscarriage is highest. The second trimester (weeks 14–27) is often when people feel their best: energy returns, nausea fades, and the first kicks begin. The third trimester (week 28 onward) is a period of rapid weight gain and lung maturation as the baby prepares for birth.

This calculator lets you enter any one of three things — your LMP, your due date, or the week you already know — and it works out the rest, including your current gestational age, due date, trimester, and how far through the 40 weeks you are. It also flags a pregnancy that has reached 42 weeks (post-term), when most providers recommend delivery.

Important: This tool provides general, educational estimates only. It is not a substitute for professional prenatal care. Every pregnancy is unique, so always follow the advice of your doctor or midwife.

Want to learn more about what is happening right now? Browse our week-by-week guide to see your baby's size and development at each stage, or try the reverse due-date calculator to estimate your LMP from a known due date.