Gestational Age
Calculate your current gestational age in weeks and days from your estimated due date. Free pregnancy calculator with trimester tracking, progress chart, and due date countdown.
About This Calculator
The Gestational Age Calculator determines how far along you are in your pregnancy by working backward from your estimated due date (EDD). Unlike traditional methods that start from the last menstrual period, this calculator uses your due date — which is often more reliably known from ultrasound dating or IVF records — to compute the current gestational age in weeks and days. It also identifies which trimester you are in, shows the estimated date of your last menstrual period, and tracks your pregnancy progress with a visual percentage complete.
How the calculation works: The calculator subtracts 280 days (the average duration of a full-term pregnancy, or 40 weeks) from your estimated due date to derive the date of the last menstrual period (LMP). It then measures the difference between the current date and that LMP date to determine gestational age. For example, if your due date is December 31 and today is October 1, the LMP would be around March 26, putting you at approximately 27 weeks of gestation. The result is displayed as weeks and days (e.g., 27w 2d).
Regional Notes: Gestational age conventions are consistent worldwide. In India, the United States, and the United Kingdom, pregnancy is measured in gestational weeks starting from the LMP. Due dates are typically estimated via ultrasound in the first trimester (crown-rump length measurement) or calculated from LMP using Naegele's rule (adding 280 days to the first day of the LMP). Healthcare providers in all three regions use the same 40-week model and trimester definitions. Ultrasound dating in the first trimester is considered the most accurate method for determining gestational age, with a margin of error of about 5–7 days.
Frequently Asked Questions
What is gestational age and how is it calculated?
Gestational age is the age of a pregnancy measured in weeks, typically calculated from the first day of the last menstrual period (LMP) to the current date. This calculator estimates gestational age from your due date by subtracting 280 days (40 weeks) to find the LMP date, then computing the difference between the current date and LMP. The result is shown in weeks and days.
How does the Gestational Age Calculator work?
Enter your estimated due date (EDD) as provided by your doctor or ultrasound, and the current date. The calculator subtracts 280 days from your due date to estimate the date of your last menstrual period, then computes the difference between today and that LMP date to determine how many weeks and days pregnant you are.
Is the gestational age the same as fetal age?
No. Gestational age is measured from the first day of the last menstrual period (about 2 weeks before conception), while fetal age (or fertilization age) is measured from the actual date of conception. Gestational age is approximately 2 weeks longer than fetal age. Most healthcare providers use gestational age for pregnancy tracking.
What are the trimesters in pregnancy?
Pregnancy is divided into three trimesters. The first trimester spans weeks 1 through 12, the second trimester spans weeks 13 through 26, and the third trimester spans weeks 27 through 40. Each trimester involves different developmental milestones and changes for both the mother and baby.
How accurate is gestational age calculation from due date?
This method assumes a standard 28-day cycle and 40-week pregnancy. Actual pregnancy duration can vary by up to 2 weeks. For the most accurate gestational age assessment, consult your healthcare provider who may use ultrasound measurements (crown-rump length) and other clinical indicators.
Can I use this calculator if I conceived through IVF?
Yes. For IVF pregnancies, your doctor will provide an estimated due date based on the embryo transfer date and the type of IVF cycle. Enter that due date into this calculator to track your gestational age. The due date from IVF is generally more precise because the conception date is known exactly.
What is the normal range for gestational age at birth?
A full-term pregnancy is typically between 39 weeks and 40 weeks and 6 days. Early term is 37 to 38 weeks and 6 days. Late term is 41 to 41 weeks and 6 days. Preterm is before 37 weeks, and postterm is 42 weeks or more. These classifications are used consistently in India, the US, and the UK.
Why does the due date matter for gestational age calculation?
The due date is the reference point for calculating gestational age backwards. Once the estimated date of delivery is known (from ultrasound, LMP, or IVF dating), the calculator derives the LMP date by subtracting 280 days, which then enables determining the current gestational age from today's date.