Use our free Gestational age Calculator to get personalized health results. Based on validated medical formulas and clinical guidelines.
Reviewed for accuracy by Rahul Singh, Health & Wellness Specialist
Reviewed for accuracy by Rahul Singh, Health & Wellness Specialist
Medical disclaimer:
This calculator is provided for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment. Results are general estimates and may not reflect your individual circumstances. Always consult a qualified healthcare professional before making decisions about your health.
Gestational Age Calculator
Calculator
Adjust values & calculate
Enter your values below. Every result is computed in your browser — no data is sent to any server.
Formula: GA = (Current Date - LMP) in weeks and days | EDD = LMP + 280 days | Adjusted for cycle length
Your Result
Worked example — 21 weeks, 6 days — Second trimester
Formula
GA = (Current Date - LMP) in weeks and days | EDD = LMP + 280 days | Adjusted for cycle length
Gestational age is calculated from the first day of the last menstrual period (LMP). Normal pregnancy = 40 weeks (280 days). If cycle length differs from 28 days, adjust by adding (cycle - 28) days to due date.
Worked Examples
Example 1: LMP March 1, 2024
Problem:LMP: March 1, current date: August 1, 28-day cycle
Problem:LMP: January 10, 2024, current date: April 10, 2024, average cycle length 35 days (7 days longer than the 28-day default).
Solution:Raw days since LMP = 91. Cycle adjustment = 35 - 28 = +7 days, so adjusted days = 91 - 7 = 84 days = 12 weeks even. Due date shifts to LMP + 287 days (280 + 7) instead of the standard 280.
Result:12 weeks, 0 days — First/Second trimester boundary; due date moved 7 days later than a standard 28-day-cycle estimate
Frequently Asked Questions
How is gestational age calculated?
GA is counted from the first day of the last menstrual period (LMP), even though conception typically occurs ~2 weeks later. This is the standard medical convention.
What does 'viable' mean in pregnancy?
Fetal viability refers to the gestational age at which a baby has a reasonable chance of survival outside the womb with medical support. This threshold is generally considered to be around 24 weeks. Survival rates at 24 weeks are roughly 50–70% with intensive care, and they improve significantly with each additional week of gestation.
Why does my ultrasound due date differ from my LMP-based due date?
First-trimester ultrasound dating (measuring crown-rump length between about 6 and 13 weeks) is considered more accurate than LMP dating alone because it does not depend on remembering the exact first day of your last period or assuming a textbook 28-day cycle with ovulation on day 14. ACOG guidance is that if the ultrasound date and LMP date disagree by more than 5 to 7 days in the first trimester (or by more than 10 days in the early second trimester), the pregnancy is typically re-dated to the ultrasound estimate, since irregular cycles, late ovulation, or an inaccurate recalled LMP are common sources of error.
What is the difference between gestational age and fetal (conceptional) age?
Gestational age counts from the first day of the last menstrual period, roughly two weeks before conception actually occurs, which is why it is sometimes called 'menstrual age.' Fetal or conceptional age counts from the estimated date of conception itself, so it runs about two weeks behind gestational age at any given point. Nearly all clinical practice, due date calculations, and Gestational Age Calculator use gestational age, but the distinction matters when comparing to some embryology references or IVF timelines, which often use conceptional/embryonic age since the fertilization date is known precisely.
What is gestational age versus fetal age?
Gestational age counts from the first day of the last menstrual period (LMP) and is the standard used in obstetrics and on due date calculators. Fetal age (also called embryonic or conceptual age) counts from the actual date of fertilization, which occurs approximately two weeks after the LMP in a standard 28-day cycle. A fetus that is 10 weeks gestational age is actually about 8 weeks old from fertilization. All prenatal appointments, growth charts, and due date estimates use gestational age by convention.
Essential site storage stays on. Analytics, performance, and marketing cookies remain off until you choose. Calculator inputs stay on your device, and we do not sell your personal data.
We use essential cookies only. Analytics cookies require your consent.
