# How many net carbs are in this?

Works out net carbs from a Nutrition Facts label: total carbohydrate minus dietary fiber and all, half or none of the sugar alcohols, per serving and for the servings you eat.

- Page: https://www.acalculator.org/food/net-carb-calculator
- JSON spec: https://www.acalculator.org/food/net-carb-calculator.json
- Version: b32b40238db5

## Default answer

Example with the default inputs (Total carbohydrate, g 46, Dietary fiber, g 7, Sugar alcohols, g 0, Subtract sugar alcohols All, Servings eaten 1): This has 39 g of net carbs per serving.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| c | Total carbohydrate, g | Total carbohydrate per serving, from the label. |
| f | Dietary fiber, g | Dietary fiber per serving, from the label. |
| sa | Sugar alcohols, g | Sugar alcohols per serving, if the label lists them (0 if not). |
| r | Subtract sugar alcohols | How much of the sugar alcohols to take off: all, half, or none. |
| n | Servings eaten | How many servings you eat; 0.5 for half a serving. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| net | Net carbs per serving (g) | Total carbohydrate − fiber − the sugar alcohols you subtract. |
| netTotal | Net carbs eaten (g) | Net carbs per serving × servings. |
| totalEaten | Total carbohydrate eaten (g) | Total carbohydrate × servings. |
| subtracted | Subtracted per serving (g) | Fiber plus the sugar alcohols you subtract. |

## Method

Net carbs = total carbohydrate − dietary fiber − sugar alcohols × (1, ½ or 0). Net carbs eaten = net carbs per serving × servings.

## Assumptions

- “Net carbs” has no FDA definition; this is the common convention. Fiber and sugar alcohols are subtracted because they are not fully digested.
- Label values are per serving and already rounded on the label.

## Worked examples

1. c = 46, f = 7, sa = 0, r = all, n = 4 gives net = 39, netTotal = 156, totalEaten = 184. Source: FDA, Interactive Nutrition Facts Label: Total Carbohydrate (includes dietary fiber, total sugars and sugar alcohols; sample label 46 g total carbohydrate, 7 g fiber, 4 servings), https://www.accessdata.fda.gov/scripts/InteractiveNutritionFactsLabel/total-carbohydrate.cfm (retrieved 2026-10-03).
2. c = 20, f = 3, sa = 10, r = half, n = 1 gives net = 12, subtracted = 8. Source: FDA, Interactive Nutrition Facts Label: Total Carbohydrate (includes dietary fiber, total sugars and sugar alcohols; sample label 46 g total carbohydrate, 7 g fiber, 4 servings), https://www.accessdata.fda.gov/scripts/InteractiveNutritionFactsLabel/total-carbohydrate.cfm (retrieved 2026-10-03).
3. c = 20, f = 3, sa = 10, r = all, n = 0.5 gives net = 7, netTotal = 3.5. Source: FDA, Interactive Nutrition Facts Label: Total Carbohydrate (includes dietary fiber, total sugars and sugar alcohols; sample label 46 g total carbohydrate, 7 g fiber, 4 servings), https://www.accessdata.fda.gov/scripts/InteractiveNutritionFactsLabel/total-carbohydrate.cfm (retrieved 2026-10-03).

## FAQ

### How do I calculate net carbs?

Take the total carbohydrate and subtract the dietary fiber. If the label lists sugar alcohols, subtract them too (or half of them, a common cautious rule). A serving with 46 g of carbohydrate and 7 g of fiber has 39 g of net carbs.

### Why subtract fiber?

Fiber is a carbohydrate that the body cannot easily digest, so it adds little to blood sugar. FDA counts it inside total carbohydrate on the label, which is why it is subtracted to get net carbs.

### Should I subtract all of the sugar alcohols?

Sugar alcohols are only partly absorbed, and the amount varies by type. Many people subtract all of them; some subtract half to be safe. Pick All, Half or None.

### Is net carbs an official number?

No. FDA does not define net carbs, and they are not on the Nutrition Facts label. The label shows total carbohydrate, dietary fiber, total and added sugars, and sometimes sugar alcohols.

### How do servings change the answer?

Label values are per serving. Eating the whole 4-serving container of the FDA sample food means 4 × 39 = 156 g of net carbs.

### Can net carbs be negative?

No. Fiber and sugar alcohols are part of the total carbohydrate, so they cannot be larger than it. The page shows no answer if they are.

## Sources

- FDA, Interactive Nutrition Facts Label: Total Carbohydrate. Total carbohydrate includes dietary fiber, total sugars and sugar alcohols; sample label with 46 g of total carbohydrate, 7 g of dietary fiber and 4 servings per container. Retrieved 2026-10-03. https://www.accessdata.fda.gov/scripts/InteractiveNutritionFactsLabel/total-carbohydrate.cfm
- FDA, How to Understand and Use the Nutrition Facts Label (serving sizes; dietary fiber DV 28 g). Retrieved 2026-10-03. https://www.fda.gov/food/nutrition-facts-label/how-understand-and-use-nutrition-facts-label