Gestational Age Calculator
Calculate gestational age in weeks and days from the last menstrual period or a known due date, for dating a pregnancy. Educational tool only.
Gestational age counts from the first day of your last period, not from conception โ which is why you are already โtwo weeks pregnantโ at conception. It assumes a 28-day cycle. Dating from a known due date simply subtracts 280 days, so it inherits any inaccuracy in that estimate. Pregnancy dating is confirmed by ultrasound, and the scan date takes precedence whenever the two disagree by more than about a week.
Frequently asked questions
How is gestational age calculated?
Gestational age is counted from the first day of your last menstrual period, not from conception, which is why the count starts about two weeks before you could actually have conceived.
What is corrected gestational age?
For babies born prematurely, corrected gestational age adjusts the age to account for the weeks they were born early. It is often used until around two years of age when assessing development.
When does each trimester start?
The first trimester runs to the end of week 13, the second from week 14 to the end of week 27, and the third from week 28 until birth.
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