Why the calculator shows three answers
On a U.S. or Canadian-style label, the starting calculation is total carbohydrate minus dietary fiber. Erythritol is then subtracted when the label gives its amount separately. Other sugar alcohols stay inside a range: count all of them for the conservative end, half for the middle estimate, or subtract all for the lowest end.
The range is deliberate. FDA labeling guidance assigns different energy factors to erythritol, maltitol, sorbitol, xylitol, mannitol, and other polyols. A single rule for every sugar alcohol hides that difference.
Choose the label format before subtracting fiber
U.S. Total Carbohydrate includes dietary fiber, so subtracting fiber once is the usual basic formula. UK and EU-style labels define carbohydrate separately from fibre. If you start from the carbohydrate line on one of those labels, subtracting fibre again counts the same deduction twice.
If your package does not match either format, use the definition printed on the package or the manufacturer's nutrition documentation.
Check the ingredient, not only the sugar-alcohol total
Erythritol has a different FDA calorie factor from maltitol, sorbitol, xylitol, and several other polyols. A package may show one combined sugar-alcohol number without telling you how much comes from each type. In that case, the label does not support a precise net-carb result.
The net-carb calculation guide walks through a U.S. example, a UK example, product claims, allulose, and the cases where total carbohydrate is the more useful number.
What this result can and cannot tell you
The result describes label arithmetic. It cannot predict digestion, ketosis, blood glucose, gastrointestinal effects, or medication needs. The American Diabetes Association notes that the net-carb equation is not entirely accurate because fibers and sugar alcohols differ.
If carbohydrate counting affects diabetes treatment or another clinical plan, use the method given by your clinician or registered dietitian. The ADA recommends total carbohydrate for blood-glucose decisions rather than relying on a package's net-carb claim.
Method and limits are based on the FDA Food Labeling Guide, FDA Nutrition Facts compliance guidance, the American Diabetes Association explanation of total and net carbohydrate, and the retained UK and EU food-information regulation.