Gestational Age Calculator (Weeks & Days Pregnant)
Use this free gestational age calculator to find out how many weeks and days pregnant you are based on your last period (LMP), due date (EDD), or ultrasound measurements like CRL or gestational sac size.
Gestational Age Calculator
If you have an early ultrasound report, CRL is often the most accurate.
Select the first day you started bleeding in your last period.
What Is Gestational Age?
Gestational age refers to how far along a pregnancy is, measured in weeks and days. Doctors and midwives typically calculate gestational age starting from the first day of your last menstrual period (LMP), which is about two weeks before conception occurs.
This is why many people search for a weeks pregnant calculator from due date or pregnancy week calculator by LMP to better understand their pregnancy timeline.
How to Calculate How Many Weeks Pregnant You Are
This gestational age calculator helps you estimate your current pregnancy week using one of the most common medical dating methods:
- LMP (Last menstrual period) — best if you know the first day of your last period
- Due date (EDD) — useful if your doctor already provided an estimated delivery date
- Ultrasound CRL — often the most accurate method in the first trimester
- Gestational sac size (GS) — used in very early pregnancy before CRL is visible
Using Ultrasound to Estimate Gestational Age (CRL Method)
An early pregnancy ultrasound is one of the most reliable ways to confirm gestational age. Clinicians often measure the Crown–rump length (CRL), which is the length of the embryo from the top of the head to the bottom of the torso.
If you have an ultrasound report showing CRL in millimeters, you can use this calculator to estimate your pregnancy week and due date more accurately.
Gestational Age Calculation Methods Comparison
| Method | Best Used For | Typical Accuracy |
|---|---|---|
| LMP (Last menstrual period) | General pregnancy dating before ultrasound | May vary by 1–2 weeks if cycles are irregular |
| Ultrasound (CRL) | First trimester dating (6–13 weeks) | Usually accurate within a few days |
| Due Date (EDD) | If you already know your estimated delivery date | High accuracy depending on how EDD was established |
Gestational Age Calculator FAQs
What is the difference between fetal age and gestational age?
Gestational age is measured from the first day of your last menstrual period (LMP), while fetal age begins at conception. Gestational age is typically about 2 weeks ahead of fetal age.
How accurate is a gestational age calculator by due date?
A due date-based gestational age calculator is usually accurate if the due date was confirmed by an early ultrasound. If the due date was estimated without imaging, accuracy may vary.
Can ultrasound dating change my due date?
Yes. In early pregnancy, ultrasound CRL measurements may adjust the estimated due date if there is a difference of several days compared with LMP dating.
How can I calculate how many weeks pregnant I am right now?
You can calculate weeks pregnant using your LMP, due date (EDD), or ultrasound measurements. This tool instantly shows your pregnancy week, days pregnant, and estimated timeline.
Medical Disclaimer
Disclaimer: This gestational age calculator provides estimates for informational purposes only. It is not a substitute for professional medical advice, diagnosis, or prenatal care. Ultrasound results should always be interpreted by a qualified healthcare provider.