Net Carbs Calculator
Calculate net carbs by subtracting fiber and sugar alcohols from total carbs, the way keto and low-carb diets count them. Net carbs are a diet convention, not an FDA-defined value, so the result is an illustration of that rule.
Reviewed & updated for 2026 by Rakesh Choudhary, PhDMethodology & sources · How we calculate
Why "net carbs" matters more than total carbs on keto
Ketosis is triggered when your liver runs out of stored glycogen and shifts to producing ketone bodies from fat. Glucose is the primary driver, the more glucose entering your bloodstream, the more insulin your body releases, and the harder it becomes to enter or stay in ketosis. Low-carb diets leave fiber and certain sugar substitutes out of the count on the reasoning that they don't raise blood glucose the way sugar and starch do.
The FDA defines dietary fiber as non-digestible carbohydrate, which is the basis for subtracting all of it. Sugar alcohols and newer sweeteners vary by type, and the FDA sets no net-carb rule for them, so this page follows a common convention: 50% of most sugar alcohols is subtracted, and all of any allulose or erythritol.
Practically: a serving labelled 15g total carbohydrate with 8g fiber counts as 7g net carbs, while one with nearly the same total (16g) but only 1g fiber counts as 15g, 75% of a 20g keto day. That difference is why low-carb diets favour high-fiber foods.
Worked examples of the net carb math
| Label example (1 serving) | Total carbs | Fiber | Sweetener subtracted | Net carbs |
|---|---|---|---|---|
| A high-fiber food | 15g | 8g | 0g | 7g |
| A low-fiber food | 16g | 1g | 0g | 15g |
| A bar with 10g maltitol | 24g | 9g | 5g | 10g |
| The same bar with 10g erythritol | 24g | 9g | 10g | 5g |
These are made-up label values to show the arithmetic, not figures for any real food. The two bars differ only in sweetener: this rule counts 10g net carbs with maltitol and 5g with erythritol. For a particular food, use the Nutrition Facts label on the package or look the food up in USDA's FoodData Central; values vary with variety and serving size.
Where net-carb math gets it wrong
- Maltitol confusion: Sugar-free candies often use maltitol heavily and label themselves "keto-friendly." Treating maltitol as zero carbs understates what the product contains; this rule counts half of it.
- Resistant starch ambiguity: Some carbs are listed as "total carbs" but contain resistant starch that doesn't digest like normal starch. Unripe bananas and cooked-and-cooled potatoes or rice contain some resistant starch, but the label doesn't say how much.
- "No added sugar" doesn't mean low carb: Fruit juice "with no added sugar" still contains the fruit's own sugars. The Nutrition Facts label lists total sugars, which include sugars naturally present in fruit and milk, separately from added sugars (FDA). Read the label, not the marketing claim.
- Labels from outside the US: on a US label, total carbohydrate includes fiber, because it is calculated by difference (21 CFR 101.9). This calculator assumes a US label. If a label from another country already excludes fiber from its carbohydrate figure, don't subtract the fiber again.
- Individual variability: Carb tolerance differs from person to person, and no single daily figure suits everyone. Use ketone strips or breath meters to verify what works for you.
FAQs
How do you calculate net carbs?
This page uses a common low-carb rule: net carbs = total carbohydrate − dietary fiber − 50% of sugar alcohols − allulose and erythritol. It is a convention, not an FDA method; the FDA does not define net carbs. On a US Nutrition Facts label, total carbohydrate is calculated by difference, so it already includes fiber and any sugar alcohols, which is why they are subtracted from it.
Should I count net carbs or total carbs?
It depends on the diet you follow. Net carbs are a low-carb diet convention; the Nutrition Facts label and the FDA's Daily Value (275g of total carbohydrate) use total carbohydrate. If you manage diabetes, set carbohydrate counting with your diabetes care team rather than from a general formula.
What about allulose and other sugar alcohols?
This page subtracts allulose and erythritol in full and other sugar alcohols (such as maltitol, xylitol and sorbitol) at 50%. That split is a convention, not an FDA rule. A US label lists sugar alcohols only voluntarily, or when the package makes a claim about sugars or sugar alcohols, so you may need the ingredient list to see what a product contains.
How many net carbs per day for keto?
There is no official figure. Strict keto plans commonly aim for about 20g of net carbs a day, which is why the calculator compares your result with 20g; that is a diet convention, not a health guideline. For comparison, the FDA's Daily Value for total carbohydrate is 275g.
Does protein count toward carbs?
No. Protein is listed separately on the Nutrition Facts label and is not part of total carbohydrate, so it does not enter this calculation. How much protein suits a low-carb diet varies; a dietitian or doctor can help you set it.