How do I know how many weeks pregnant I am?

Enter your estimated due date (EDD) in the calculator. The calculator works backward from your due date (assuming a 40-week pregnancy) to determine your current gestational age. You can get your EDD from your healthcare provider or use our Due Date Calculator.

What are the trimester boundaries?

The first trimester runs from weeks 0-12 (conception through week 12). The second trimester runs from weeks 13-27. The third trimester runs from week 28 through delivery. These boundaries reflect the major developmental stages of pregnancy.

What is gestational age vs. fetal age?

Gestational age counts from the first day of your last menstrual period (LMP), which is typically about 2 weeks before conception. Fetal age (also called fertilization age) counts from conception. Most medical dating uses gestational age, so when your provider says "20 weeks," that's gestational age.

When do most women start showing?

Most first-time mothers start showing between weeks 12-16, though it varies widely. Women who have been pregnant before may show earlier. Your uterus rises above the pubic bone around week 12 and is at the level of the navel around week 20.

What is fetal viability?

Fetal viability refers to the ability of a fetus to survive outside the womb with medical support. This threshold is generally considered to be around 22-24 weeks of gestational age. Survival rates improve significantly with each additional week of development beyond this point.

Pregnancy Week Calculator

Find out exactly how far along you are — see your current week, trimester, progress bar, and this week's fetal development.

"How far along am I?" is one of the most common questions during pregnancy. This pregnancy week calculator instantly shows your current gestational week, trimester, and a visual progress bar based on your estimated due date — no manual counting required.

Understanding your exact week of pregnancy helps you track fetal development milestones, anticipate upcoming prenatal screenings, and prepare for each stage of your journey. Enter your due date from your healthcare provider or use our Due Date Calculator first if you need one.

ACOG gestational age standardsStandard 40-week pregnancy modelTrimester boundaries per clinical definitions

Understanding Your Pregnancy Week

Your gestational age is displayed in weeks and days (e.g., "24 weeks, 3 days"). This is the standard dating system used by all healthcare providers — it counts from the first day of your last menstrual period (LMP), which is approximately 2 weeks before actual conception.

The trimester indicator tells you which major phase of pregnancy you are in. The first trimester (weeks 1-12) covers early organ formation, the second trimester (weeks 13-27) brings rapid growth and the first felt movements, and the third trimester (weeks 28-40) focuses on lung maturation and final weight gain.

The progress bar shows your percentage through the full 40-week pregnancy. At 20 weeks you are halfway, at 28 weeks (third trimester start) you are 70% complete, and at 37 weeks you reach "early term" — the point at which most babies can be safely delivered.

The fetal development summary provides a snapshot of what is happening with your baby this week — key milestones like organ development, sensory capabilities, and approximate size comparisons to help you visualize growth.

How Pregnancy Weeks Are Counted

Pregnancy is measured in gestational weeks, counted from the first day of your last menstrual period (LMP) — not from conception. This means gestational week 1 begins before you are technically pregnant, and conception typically occurs around week 2.

This calculator works backward from your estimated due date (EDD). Since the standard pregnancy is 280 days (40 weeks) from LMP, we subtract 280 days from your EDD to estimate your LMP equivalent, then count forward to today to determine your current gestational age.

The trimester boundaries used follow standard ACOG clinical definitions: first trimester covers weeks 1-12, second trimester covers weeks 13-27, and third trimester covers weeks 28 through delivery.

Formulas

LMP equivalent = EDD − 280 days

Gestational age (days) = Today − LMP equivalent

Weeks = floor(Gestational age ÷ 7)

Remaining days = Gestational age mod 7

Progress = (Gestational age ÷ 280) × 100%

Assumptions

Standard pregnancy duration is 280 days (40 weeks) from LMP
The due date provided is based on a 40-week pregnancy model
Trimester boundaries follow ACOG clinical definitions (12/27/40 weeks)
Gestational age, not fetal age, is used for all calculations (standard medical convention)

Limitations & Edge Cases

Pregnancies beyond 42 weeks (post-term) are flagged — ACOG recommends delivery by this point
If the calculated LMP is in the future, the pregnancy has not yet started
Fetal development summaries are approximations — individual variation is normal
The calculator does not account for pregnancies that may deliver earlier due to medical conditions

Sources

ACOG Committee Opinion No. 700 — Methods for Estimating Due Date
ACOG — Definition of Term Pregnancy (Obstet Gynecol. 2013)

Frequently Asked Questions

Related Calculators

Due Date Calculator

Calculate your estimated due date from LMP, conception date, IVF transfer, or ultrasound. Supports twins.

Trimester Calculator

See your trimester stages with exact date ranges and key developmental milestones.

Pregnancy Month Calculator

Convert pregnancy weeks to months with trimester mapping and calendar dates.

Pregnancy Timeline Generator

View your complete 40-week pregnancy calendar with appointments, screenings, and milestones.

Related Guides

How Due Dates Are Calculated (And Why They Change)

Explains Naegele's rule, LMP-based dating, ultrasound adjustment, and why your due date may shift during pregnancy. What to expect at each dating appointment.

Your Pregnancy Week by Week: What to Expect

A week-by-week pregnancy guide covering fetal development, common symptoms, key appointments, and what changes to expect at each stage from conception to birth.

Understanding Trimester Milestones

Key milestones and fetal development stages for each trimester. Covers first-trimester viability, second-trimester anatomy scan, and third-trimester growth and birth preparation.

This calculator provides estimates for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your healthcare provider with questions about your health or your baby's health.

Based on standard 40-week pregnancy model per ACOG guidelines.