Net carb calculator
Net carbs are total carbohydrate minus fiber. Type the numbers from a label, or fill them from a USDA food at its typical portion. FDA has not defined net carbs; some packages also subtract sugar alcohols, which the third field lets you do.
48.5 gnet carbs (carbohydrate minus fiber)
Source: USDA FoodData Central for the foods; the label's Total Carbohydrate and Dietary Fiber lines (21 CFR 101.9(c)(6)).
Which number to use
Carbohydrate minus fiber is the count GetFoodFacts uses on every page and list, because both numbers are on every label. Sugar alcohols (erythritol, maltitol, sorbitol) are carbohydrates the body absorbs in part; subtracting them is the manufacturer's choice, not an FDA rule. Nothing you type leaves your browser.