Gestational Age Calculator - Calculate Pregnancy Weeks
Calculate gestational age in weeks and days based on last menstrual period or ultrasound dating to track pregnancy progress and determine due date
Gestational Age Calculator
Gestational Age Results
What is a Gestational Age Calculator?
A Gestational Age Calculator is a medical tool that determines how far along a pregnancy is by calculating the number of weeks and days since the first day of the last menstrual period (LMP) or based on ultrasound measurements. It helps track pregnancy progress and estimate the due date.
This calculator helps you:
- Track pregnancy progress - Monitor how many weeks pregnant you are
- Determine trimester - Know which pregnancy stage you're in
- Estimate due date - Calculate when your baby is expected
- Plan prenatal care - Schedule important medical appointments
To calculate your exact due date and track important pregnancy milestones, check out our Pregnancy Due Date Calculator to see trimester transitions and full-term dates.
For tracking your menstrual cycle and fertile windows, explore our Period Calculator to predict ovulation and plan conception timing.
To maintain healthy weight during pregnancy, use our BMI Calculator to monitor body mass index and ensure optimal maternal health.
For calculating daily caloric needs during pregnancy, try our TDEE Calculator to determine energy expenditure and nutrition requirements.
To determine your ideal pre-pregnancy weight, check our Ideal Body Weight Calculator to establish healthy weight goals for conception planning.
How Gestational Age Calculator Works
The calculation uses two primary methods:
LMP Method:
Ultrasound Method:
Where:
- LMP = First day of last menstrual period
- Gestational Age = Weeks and days pregnant
- Due Date = LMP + 280 days (40 weeks)
Key Pregnancy Concepts Explained
Gestational Age
Pregnancy duration measured from the first day of your last menstrual period, typically 40 weeks (280 days).
Fetal Age
Actual age of the baby calculated from conception, typically 2 weeks less than gestational age.
Trimesters
Pregnancy divided into three stages: 1st (0-13 weeks), 2nd (14-27 weeks), 3rd (28-40 weeks).
Due Date Accuracy
Only 5% of babies are born on their exact due date. Most births occur within 2 weeks before or after.
How to Use This Calculator
Choose Method
Select LMP or ultrasound dating method
Enter Date
Input LMP date or ultrasound information
Set Cycle Length
Adjust if different from 28 days (LMP method)
View Results
See gestational age, trimester, and due date
Benefits of Tracking Gestational Age
- • Prenatal Care Planning: Schedule ultrasounds, blood tests, and checkups at the right gestational age.
- • Milestone Tracking: Monitor baby's development week by week and understand growth stages.
- • Medical Decision Making: Help healthcare providers determine appropriate interventions and timing.
- • Birth Preparation: Plan maternity leave, hospital arrangements, and delivery preparations.
Factors That Affect Accuracy
1. Menstrual Cycle Regularity
Irregular cycles can affect LMP-based calculations. Women with cycles shorter or longer than 28 days may ovulate at different times.
2. Ovulation Timing
Ovulation doesn't always occur on day 14. Early or late ovulation affects conception date and gestational age accuracy.
3. Ultrasound Timing
First-trimester ultrasounds (8-13 weeks) are most accurate. Later ultrasounds have wider margins of error.
Frequently Asked Questions (FAQ)
Q: How accurate is gestational age calculation?
A: Gestational age calculations based on LMP are accurate within 1-2 weeks for women with regular cycles. Ultrasound dating in the first trimester is the most accurate method, with precision within 3-5 days.
Q: What's the difference between gestational age and fetal age?
A: Gestational age is calculated from the first day of your last menstrual period (LMP), while fetal age is calculated from conception. Gestational age is typically 2 weeks longer than fetal age.
Q: Can I use this calculator if I have irregular periods?
A: If you have irregular periods, the LMP method may be less accurate. The ultrasound dating method is recommended for more precise results. Consult your healthcare provider for confirmation.
Q: When should gestational age be confirmed by ultrasound?
A: Gestational age should be confirmed by ultrasound during the first trimester (8-13 weeks) for maximum accuracy. Early ultrasounds provide the most reliable dating for pregnancy.