Gestational Age Calculator
Use our free Gestational age Calculator to get personalized health results. Based on validated medical formulas and clinical guidelines.
Reviewed by Rahul Singh, Health & Wellness Specialist
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
Solution:Days: 153. GA: 21 weeks, 6 days. Due: Dec 6, 2024
Result:21 weeks, 6 days — Second trimester
Example 2: Longer Cycle Adjustment
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
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.
References
Reviewed by Rahul Singh, Health & Wellness Specialist · Editorial policy