Gestational Age Calculator

About the Gestational Age Calculator

Gestational age (GA) is the standard way pregnancy progress is recorded in charts, ultrasound reports, and prenatal scheduling. It is measured from the first day of the last menstrual period, not from conception, which is why gestational age is usually about two weeks ahead of fetal age.

This calculator shows your GA in weeks and days, the total number of pregnancy days, and an approximate fetal age. That gives you the same language your OB, midwife, ultrasound report, and pregnancy guidance materials use.

Knowing the current GA helps you place screening windows, growth expectations, and delivery timing on the right calendar.

When This Page Helps

Gestational age is the reference point for nearly every prenatal milestone: nuchal translucency timing, anatomy scan timing, glucose screening, fetal-growth checks, and delivery planning. If you know the exact week and day, it is easier to interpret what a provider means when they say a pregnancy is 11w3d, early term, or post-term.

How to Use the Inputs

1. Enter the first day of your last menstrual period (LMP).
2. The calculator displays your current gestational age in weeks and days.
3. View additional details including fetal age, total days, and milestones.
4. Compare with your most recent ultrasound report to verify consistency.
5. Check back regularly to track your changing gestational age.

Example Calculation

Tips & Best Practices

• Gestational age is always about 2 weeks more than fetal age (age since conception).
• ACOG defines full term as 39 weeks 0 days through 40 weeks 6 days.
• Preterm is before 37 weeks; early term is 37w0d to 38w6d; late term is 41w0d to 41w6d.
• If your ultrasound GA differs from LMP GA by more than 7 days (first trimester), the ultrasound date may be used.
• Write your GA on the top of your birth plan so care providers know your exact dates.

Understanding Gestational Age Notation

Gestational age is written as weeks + days, such as 10w3d (10 weeks and 3 days). The week number starts from 0 at LMP and progresses to 40 at the due date. You are "in your 11th week" when your GA reads 10w0d through 10w6d.

GA and Prenatal Screening Windows

Many critical pregnancy tests have narrow GA windows. The nuchal translucency scan must be done between 11w0d and 13w6d. The quad screen is drawn between 15w0d and 22w6d. The glucose challenge test is typically at 24w0d to 28w0d. Knowing your exact GA ensures these tests happen at the right time.

GA and Delivery Timing

ACOG defines delivery categories by GA: preterm (<37w), early term (37w-38w6d), full term (39w-40w6d), late term (41w-41w6d), and post-term (≥42w). Elective delivery before 39 weeks is generally discouraged unless medically indicated.

Frequently Asked Questions

• What is the difference between gestational age and fetal age?

  Gestational age (GA) counts from the first day of your LMP and includes about 2 weeks before conception. Fetal age counts from the actual date of conception. A pregnancy at 10 weeks GA has a fetus that is approximately 8 weeks old.

• Why do doctors use gestational age instead of fetal age?

  Because the LMP is a known, datable event for most women, while the exact moment of conception is rarely known. Using the LMP provides a consistent starting point. This convention has been standard for over a century.

• What milestones correspond to which gestational age?

  Key milestones include: heartbeat visible at 6-7 weeks, all organs forming by 8 weeks, end of first trimester at 12 weeks, quickening at 16-22 weeks, viability at 24 weeks, and full term at 39 weeks. Knowing these milestones helps you track your baby's development and understand the timing of important prenatal screenings.

• Is 40 weeks exactly 9 months?

  Not exactly. 40 weeks is 280 days, which is about 9 months and 7 days. The discrepancy arises because calendar months vary in length from 28 to 31 days, while pregnancy is measured in fixed 7-day weeks.

• Can gestational age be corrected after birth?

  Yes. The New Ballard Score assesses a newborn's physical and neuromuscular maturity to estimate gestational age at birth. This is useful when prenatal dating is uncertain.

• What does EGA mean on my chart?

  EGA stands for Estimated Gestational Age. It is the same as GA but emphasizes that it is an estimate. You may also see EDC (Estimated Date of Confinement), which is an older term for EDD.