How many net carbs are in this?
Copy the total carbohydrate, dietary fiber and sugar alcohols from a Nutrition Facts label. The net carb calculator subtracts them and shows the net carbs per serving and for the servings you eat.
- Net carbs per serving (g)
- 39
This has 39 g of net carbs per serving.
- Net carbs eaten (g)
- 39
- Total carbohydrate eaten (g)
- 46
- Subtracted per serving (g)
- 7
Net carbs per serving (g): 39. This has 39 g of net carbs per serving.
How to calculate
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.
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.
Method: Net carbs = total carbohydrate − dietary fiber − sugar alcohols × (1, ½ or 0). Net carbs eaten = net carbs per serving × servings.
- “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
Each example is checked against the calculator on every build.
- Total carbohydrate, g 46, Dietary fiber, g 7, Sugar alcohols, g 0, Subtract sugar alcohols All, Servings eaten 4 gives Net carbs per serving (g) 39, Net carbs eaten (g) 156, Total carbohydrate eaten (g) 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)
- Total carbohydrate, g 20, Dietary fiber, g 3, Sugar alcohols, g 10, Subtract sugar alcohols Half, Servings eaten 1 gives Net carbs per serving (g) 12, Subtracted per serving (g) 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)
- Total carbohydrate, g 20, Dietary fiber, g 3, Sugar alcohols, g 10, Subtract sugar alcohols All, Servings eaten 0.5 gives Net carbs per serving (g) 7, Net carbs eaten (g) 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)
How it works
Net carbs are not defined by FDA. This page uses the common convention:
net carbs per serving = total carbohydrate − dietary fiber − sugar alcohols × s
where s is 1 (subtract all), ½ (subtract half) or 0 (subtract none). Then
net carbs eaten = net carbs per serving × servings, and total carbohydrate eaten = total carbohydrate × servings.
All values are in grams per serving, as on the label.
Exact arithmetic. Each value is read as the exact decimal you typed, so each result is exact until it is rounded for display.
Output format. Every value shows in grams to 1 decimal place.
When there is no answer. Fiber plus sugar alcohols is more than the total carbohydrate. Both are part of the total, so the label values must be wrong or mistyped.
Assumptions
- The label values are per serving and already rounded by the maker.
- Fiber and the chosen share of sugar alcohols add no digestible carbohydrate.
- Nothing else is subtracted. Some low-carb plans also take off allulose, a rare sugar counted in total carbohydrate; this page leaves it in.
Worked examples by hand
The FDA sample label. 46 − 7 = 39 g per serving; 4 servings: 39 × 4 = 156 g net, 46 × 4 = 184 g total.
A bar with sugar alcohols, half subtracted. 20 − 3 − 10 × ½ = 20 − 8 = 12 g.
The same bar, all subtracted, half a serving. 20 − 3 − 10 = 7 g; × 0.5 = 3.5 g.
Other questions people ask
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.