Authoritative Data Source and Methodology
Primary reference: U.S. Food & Drug Administration, “Food Labeling: Revision of the Nutrition and Supplement Facts Labels,” Final Rule, 81 FR 33742 (May 27, 2016). See 21 CFR 101.9 for definitions of Total Carbohydrate and Dietary Fiber. Direct link: https://www.ecfr.gov/current/title-21/part-101
Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.
The Formula Explained
\[ \text{NetCarbs} = C_{\text{total}} - F - f_{sa}\times SA \]
where:
\[ f_{sa} \in \{\,1.0\;(\text{subtract all}),\;0.5\;(\text{subtract half}),\;0\;(\text{subtract none})\,\} \] Servings:
\[ \text{NetCarbs}_{\text{total}} = \text{NetCarbs} \times n_{\text{servings}} \] Per 100 g (if serving mass is known):
\[ \text{NetCarbs}_{100g} = \text{NetCarbs} \times \frac{100}{m_{\text{serv}}(\mathrm{g})} \]
Glossary of Variables
| Symbol / Field | Definition |
|---|---|
| C_total (Total Carbohydrate) | All carbohydrates on the label (includes sugar, starch, and fiber), in grams per serving. |
| F (Dietary Fiber) | Non-digestible carbohydrates listed as dietary fiber, in grams per serving. |
| SA (Sugar alcohols) | Polyols such as erythritol, xylitol, maltitol, sorbitol, etc., in grams per serving. |
| f_sa | Adjustment factor for sugar alcohols: 1.0 (subtract all), 0.5 (subtract half), or 0 (subtract none). |
| n_servings | Number of servings consumed. |
| m_serv (g) | Serving mass in grams; used to scale to per 100 g. |
| NetCarbs | Carbs expected to impact blood glucose per serving (clamped at 0 minimum). |
How It Works: A Step-by-Step Example
Scenario. Label shows: Total Carbohydrate = 23 g, Dietary Fiber = 9 g, Sugar alcohols = 12 g. Choose “Subtract 50%” for sugar alcohols.
Apply the formula: NetCarbs = 23 − 9 − 0.5 × 12 = 23 − 9 − 6 = 8 g per serving. If you eat 1.5 servings, NetCarbs_total = 8 × 1.5 = 12 g.
Frequently Asked Questions (FAQ)
What are net carbs?
Net carbs estimate carbohydrate grams that meaningfully impact blood glucose: total carbohydrate minus fiber and some or all sugar alcohols.
Which sugar alcohols should I subtract fully?
Erythritol is commonly subtracted 100% due to negligible glycemic impact. For others (e.g., maltitol, sorbitol), many people count 50%. Individual responses vary.
Is allulose a sugar alcohol?
No. Allulose is a rare sugar. In US labeling, it can be excluded from total sugars count. Many low-carb methods subtract it fully from net carbs.
Can net carbs be negative?
They should not. If the calculation yields a negative value, this tool sets it to 0.
Does this replace medical advice?
No. It’s an educational calculator. Consult a qualified professional for personalized nutrition guidance.
Why is my per 100 g result blank?
You must provide serving size in grams (or ounces) so the calculator can scale a serving to 100 g.
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Last reviewed for accuracy on: .