Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Net Carbs Are Calculated
Net carbs is an estimate of the carbohydrate in a food that raises blood glucose: total carbohydrate minus fiber and some or all of the sugar alcohols. On a US nutrition label, total carbohydrate includes starch, sugars, sugar alcohols and fiber¹. Fiber isn't digested and absorbed as glucose the way other carbohydrates are, and sugar alcohols are absorbed and metabolized to varying degrees depending on which one it is².
What This Calculator Measures
This estimates net carbs from the total carbohydrate, fiber, and sugar alcohol values already printed on a nutrition label. It's a practical estimate for low-carb tracking, not a value that appears on the label itself.
The Formula
Net carbs = Total carbohydrate − Fiber − (Sugar alcohols × absorption discount)
Fiber is subtracted in full, since it isn't digested and absorbed as glucose. Sugar alcohols are subtracted at a discount rather than in full, because they vary widely in how much they actually affect blood glucose.
In this calculator the discount depends on the type you pick: erythritol is subtracted in full, while xylitol, sorbitol, maltitol and Other / Mixed are each subtracted at 50%. The result is shown to one decimal place and never goes below zero.
How This Calculator Computes Your Result
Enter total carbohydrate, fiber, and sugar alcohols (if listed) from a nutrition label. We subtract fiber in full and apply a partial discount to sugar alcohols, then show the resulting net carb estimate.
Sugar alcohols are optional on most US labels. A manufacturer has to list them only when the label makes a claim about sugar alcohols or total sugars, or about added sugars when sugar alcohols are present, and the line may name the specific sugar alcohol when the food contains only one³. If the line is missing, check the ingredient list. The calculator stops with an error if fiber plus sugar alcohols is more than total carbohydrate, since that usually means a typo.
Worked Example
A protein bar label lists 24g total carbohydrate, 9g dietary fiber and 10g sugar alcohols, and the ingredients show maltitol:
Net carbs = 24 − 9 − (10 × 0.5) = 10g
If the sugar alcohol were erythritol, the full 10g would come off and the result would be 5g. That is why the calculator asks for the type. If you track against a daily net carb cap, our keto calculator can set one.
Why Sugar Alcohols Aren't All Treated the Same
This is the part most simplified net-carb calculations get wrong. Not all sugar alcohols behave the same way in the body. Erythritol is almost completely absorbed and then excreted unchanged in the urine⁴, and its glycemic index is 0², so it is close to metabolically inert for most people.
Maltitol, by contrast, has the highest glycemic index of the sugar alcohols this calculator lists, though it is still well below table sugar². A single flat discount factor applied to every sugar alcohol is a simplification, and where the ingredient list is known, accounting for which specific sugar alcohol is present gives a more accurate estimate than treating them all identically.
Glycemic Index of Common Sugar Alcohols
A review of published blood glucose studies gave these glycemic index values, where glucose is 100²:
Sweetener | Glycemic index | Calculator subtracts |
Erythritol | 0 | 100% |
Sorbitol | 9 | 50% |
Xylitol | 13 | 50% |
Maltitol | 35 | 50% |
Table sugar (sucrose) | 65 | Not subtracted |
All of these sugar alcohols raise blood glucose less than table sugar², but they differ from each other. The calculator's 50% factor is a convention, not a measured value, and it treats xylitol, sorbitol and maltitol the same even though maltitol has the highest glycemic index of the three².
Why Net Carbs Is Not on the Label
When the FDA revised the Nutrition Facts label in 2016, some comments asked it to take fiber out of total carbohydrate, calling the result net carbs and saying it helps people with diabetes control blood glucose. The FDA declined. It kept total carbohydrate as starch, sugars, sugar alcohols and fiber, said people who want carbohydrate minus fiber can work it out from the label, and noted that the label is not aimed at people with conditions such as diabetes¹.
The FDA's labeling rule covers total carbohydrate, dietary fiber, total sugars, added sugars and sugar alcohols, but has no net carbs value³. A net carbs number on the front of a package is the maker's own calculation.
A Note on Accuracy
"Net carbs" is not an FDA-regulated or scientifically standardized term. This calculator uses the common fiber-and-sugar-alcohol subtraction method, but this is a widely used convention, not an official value. For a person with diabetes managing blood glucose directly, individual glycemic response to specific fiber types and sugar alcohols can vary meaningfully, this is a general estimate, not a substitute for personal glucose monitoring.
Frequently Asked Questions
Is net carbs an official nutrition label value?
No. It's a widely used convention in the low-carb and keto community, not a value the FDA requires or defines on nutrition labels. The FDA has declined requests to take fiber out of the label's total carbohydrate figure¹.
Why is fiber subtracted but sugar alcohols only partially subtracted?
Fiber isn't digested and absorbed as glucose, so it's subtracted in full. Sugar alcohols vary considerably, some (like erythritol) have minimal blood glucose impact, while others (like maltitol) have a larger effect², so a partial discount is a more honest estimate than treating all sugar alcohols as fully inert.
Does this work the same for everyone, including people with diabetes?
Not necessarily. Individual glycemic response to specific fiber types and sugar alcohols can vary meaningfully between people. This is a general estimate, not a substitute for personal blood glucose monitoring.
Why don't different apps and brands agree on net carbs for the same food?
Because there's no single official method. Different tools use different sugar alcohol discount assumptions, and some skip the discount for certain sugar alcohols entirely, which is exactly why results can vary between sources for the same product.
Sources
Food Labeling: Revision of the Nutrition and Supplement Facts Labels (Final Rule), U.S. Food and Drug Administration, Federal Register, 2016
Health Potential of Polyols as Sugar Replacers, With Emphasis on Low Glycaemic Properties, Livesey, Nutrition Research Reviews, 2003
21 CFR 101.9: Nutrition Labeling of Food, U.S. Food and Drug Administration, Code of Federal Regulations
Erythritol: An Interpretive Summary of Biochemical, Metabolic, Toxicological and Clinical Data, Munro et al., Food and Chemical Toxicology, 1998