Net Carbs Calculator
Work out net carbs from a US nutrition label. Enter total carbohydrate, fiber, and sugar alcohols in grams per serving, choose the sweetener type (erythritol and allulose subtract fully; maltitol-type only half), and set how many servings you ate.
Example: with Total carbohydrate (g per serving) 30 · Dietary fiber (g) 12 · Sugar alcohols / allulose (g) 5 · Sweetener type Erythritol or allulose — subtract 100% · Servings eaten 1 → Net carbs (what you ate): 13 g net carbs.
- Net carbs per serving13 g per serving
- Share of a 20 g/day strict keto budget65% of 20 g
Computed by the calculator below using its default values. Change any input to see your own numbers.
Net carbs = total carbs − fiber − sugar alcohols (100% for erythritol/allulose, 50% for maltitol-type). A convention of low-carb dieting, not an FDA-defined value.
What counting 'net' actually assumes
US nutrition labels fold fiber and sugar alcohols into Total Carbohydrate, even though your body extracts little or no glucose from them. Net carbs back those grams out to approximate the carbs that actually move blood sugar: subtract all the fiber, subtract all of erythritol or allulose (they pass through almost unmetabolized), but only half of maltitol-type sugar alcohols — maltitol has a glycemic index around 35, which is why 'sugar-free' candy can stall a keto diet.
Note the geography: this arithmetic is for US labels. UK and EU labels already exclude fiber from the carbohydrate line, so subtracting it again double-counts. 'Net carbs' is a dieting convention, not an FDA-defined nutrient — brands calculate it inconsistently, which is why doing it yourself is worth the ten seconds.
How it’s calculated
Net carbs per serving = total carbohydrate − dietary fiber − sugar alcohols, where erythritol and allulose subtract at 100% and maltitol-type polyols (maltitol, sorbitol, xylitol, isomalt) subtract at 50% — the standard keto-community convention reflecting their partial absorption (maltitol GI ≈ 35). Total = per-serving net × servings eaten. Results clamp at 0 when label rounding makes deductions exceed the total. Keto context uses a 20 g/day strict budget.
Fiber types and individual gut responses differ — some 'fiber' (like IMO syrup) raises blood sugar in many people — so net carbs are an estimate, not a guarantee, and none of this is medical advice; people managing diabetes with medication should count with their clinician's method.
Net carbs on typical US labels
| Food (serving) | Total carbs | Fiber | Sugar alcohols | Net carbs |
|---|---|---|---|---|
| Raspberries, 1 cup | 15 g | 8 g | 0 | 7 g |
| Avocado, 1 medium | 17 g | 13 g | 0 | 4 g |
| Almonds, 1 oz | 6 g | 3.5 g | 0 | 2.5 g |
| Broccoli, 1 cup | 6 g | 2.4 g | 0 | 3.6 g |
| Sugar-free chocolate, 40 g (maltitol) | 23 g | 1 g | 18 g (×50%) | 13 g |
Typical label values per USDA FoodData Central; net = total − fiber − sugar alcohols (half for maltitol-type); rounded.
Common mistakes
- Subtracting fiber from a UK/EU label — those already exclude it, so you would count carbs twice.
- Deducting maltitol at 100%: at GI ≈ 35 it is closer to half a carb than zero, and it is the most common 'sugar-free' sweetener.
- Ignoring servings — a '2 net carb' bar eaten three at a time is 6, plus label rounding on each.
- Trusting front-of-package 'net carb' claims; brands may deduct ingredients (like IMO fiber syrup) that raise blood sugar.
Frequently asked questions
How do I calculate net carbs?
Take total carbohydrate from the US label, subtract all dietary fiber, subtract all erythritol or allulose, and subtract half of any other sugar alcohol (maltitol, sorbitol, xylitol). A label with 30 g total, 12 g fiber, and 5 g erythritol is 13 g net.
Why only subtract half of maltitol?
Maltitol is partially digested and has a glycemic index around 35 — roughly half of table sugar's — so counting it as zero understates its blood-sugar effect. Erythritol and allulose, by contrast, are absorbed but not metabolized, so they subtract fully.
Do net carbs work the same on UK or EU labels?
No. Outside the US, the carbohydrate line already excludes fiber, so you only adjust for sugar alcohols. Subtracting fiber again is the most common net-carb mistake travelers make.
How many net carbs keep you in ketosis?
The common strict target is 20 g of net carbs per day, with many people maintaining ketosis at 20-50 g depending on size, activity, and metabolism. The calculator shows each food as a share of the 20 g budget.
Should diabetics count net or total carbs?
That depends on your treatment — insulin dosing formulas often use total carbs, and fiber/polyol responses vary by person. Set the counting method with your doctor, diabetes educator, or dietitian rather than adopting the keto convention by default.