Pregnancy
Gestational Age Calculator
PanaKit's gestational age calculator works five ways, from your last period, due date, an ultrasound measurement, conception date, or corrected age for babies born premature. Pick whichever you know. Runs instantly in your browser, and nothing you enter is stored or sent anywhere.
Calculate Gestational Age
Gestational age today and due date from your period start.
Enter the fields for your selected mode. Results stay on this device.
Choose a mode and enter dates to see your estimate.
How it's calculated
Gestational age is counted from the first day of your last menstrual period, not from conception, and is expressed in completed weeks and days. The LMP based method assumes a 28 day cycle and adds the elapsed time since LMP. Ultrasound based dating uses direct fetal measurements, most accurately in the first trimester using crown-rump length (CRL), and is generally considered more reliable than LMP alone, especially with irregular cycles. For babies born prematurely, corrected age (also called adjusted age) subtracts the number of weeks born early from chronological age, giving a more accurate picture for tracking developmental milestones.
Frequently asked questions
Gestational age counts from your last menstrual period. Fetal age (also called conception age) counts from the actual conception date, roughly two weeks later. A baby at 10 weeks gestational age is about 8 weeks fetal age. For the fuller explanation, see gestational age vs fetal age.
Very accurate in the first trimester, typically within 3 to 5 days, when based on crown-rump length. Accuracy decreases somewhat in later trimesters, since growth variation between babies increases as pregnancy progresses.
Corrected age adjusts a premature baby's chronological age by subtracting how many weeks early they were born. It's used to set realistic expectations for developmental milestones, since a baby born 8 weeks early is developmentally closer to their corrected age than their actual birth date would suggest.
This is common, especially with irregular cycles or an uncertain LMP date. Ultrasound measures the fetus directly, so when the two disagree by more than about a week, the ultrasound based estimate is generally considered more accurate.