Gestational Age Calculator
Calculate your precise gestational age in weeks and days using your LMP, conception date, or ultrasound measurements. See your trimester, due date, and days remaining.
How It Works
This calculator supports three methods to determine your current gestational age:
- LMP Method – Enter the first day of your last menstrual period. Gestational age is calculated as the number of days from that date to today, then converted to weeks and days.
- Conception Date – If you know your conception date (from IVF or tracked ovulation), the calculator adds 14 days to estimate an equivalent LMP, then calculates from there.
- Ultrasound Method – Enter the date of your ultrasound and the gestational age measured at that time. The calculator estimates your LMP based on the ultrasound findings, then projects your current gestational age forward.
The estimated due date is calculated as 280 days (40 weeks) from the estimated LMP date, following Naegele's rule. Results include your trimester, a visual progress bar, and the number of days remaining until your due date.
Frequently Asked Questions
What is gestational age?
Gestational age is the term used to describe how far along a pregnancy is, measured in weeks and days from the first day of the mother's last menstrual period (LMP). It's the standard way healthcare providers date a pregnancy, even though conception typically occurs about 2 weeks after the LMP.
How is gestational age different from fetal age?
Gestational age is counted from the first day of the last menstrual period, while fetal age (also called conceptional age) is counted from the actual date of conception. Fetal age is typically about 2 weeks less than gestational age because ovulation and conception occur roughly 14 days after the start of the last period.
Which method of calculating gestational age is most accurate?
First-trimester ultrasound (before 13 weeks) is generally considered the most accurate method, with accuracy within 5-7 days. LMP-based dating is reliable when periods are regular. Later ultrasounds become less precise for dating as babies grow at different rates. Your provider may adjust your due date based on early ultrasound findings.
Can gestational age change after an ultrasound?
Yes. If an early ultrasound shows a significant discrepancy (usually more than 7 days) from the LMP-based gestational age, your healthcare provider may adjust your estimated due date. This is because ultrasound measurements in the first trimester are very reliable for dating purposes.
Why does my gestational age start before conception?
Because it's measured from the first day of your last menstrual period (LMP), not from conception. This is a medical convention used because the LMP date is usually known and easily recalled, while the exact conception date is often uncertain. The first ~2 weeks of 'gestational age' occur before the egg is even fertilized.
Medical Disclaimer
This calculator is for informational purposes only and is not a substitute for professional medical advice. Always consult your healthcare provider for medical decisions regarding your pregnancy.