What this calculator does
Net carbs subtracts from total carbohydrate the parts that are not digested the same way: fibre, which is not absorbed at all, and sugar alcohols, which are absorbed only partially. It is the figure low-carb and ketogenic diets count.
Fibre does most of the work. A 30 g total with 5 g of fibre gives 25.0 g net, and one with 12 g of fibre gives 18.0 g, which is why high-fibre foods fit into a low-carb count far better than their label suggests.
The formula
Subtract fibre in full and half of any sugar alcohols from total carbohydrate. The half convention reflects that sugar alcohols are partially absorbed, with the result floored at zero.
| Term | Meaning |
|---|---|
| Net carbs | Total carbohydrate less fibre and half of sugar alcohols. |
| Sugar alcohols | Polyols such as erythritol, xylitol and maltitol, absorbed to varying degrees. |
| Convention | Net carbs is a dietary practice, not a regulated nutrition figure. |
The inputs explained
| Field | What to enter |
|---|---|
| Total carbohydrate (g) | Total carbohydrate in grams, from the nutrition label. |
| Fibre (g) | Dietary fibre in grams, subtracted in full. |
| Sugar alcohols (g) | Sugar alcohols in grams, of which half is subtracted. |
When to use it
Counting carbohydrate on a low-carb diet
Net carbs is the figure most low-carb and ketogenic plans track.
Reading a nutrition label
Labels report total carbohydrate, so the deduction has to be done yourself in many countries.
Comparing two products
Two foods with the same total carbohydrate can differ substantially once fibre is accounted for.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How much does fibre reduce the count?
The same total carbohydrate at three fibre levels.
Questions
Is net carbs an official figure?
No. It is a dietary convention rather than a regulated nutrition value, and different plans and manufacturers calculate it differently. Labels in some countries already exclude fibre from the carbohydrate figure, which changes the arithmetic entirely.
Why subtract only half of sugar alcohols?
Because they are partially absorbed, and the half convention is a rough average across the group. Individual polyols differ considerably: erythritol is largely unabsorbed while maltitol raises blood glucose meaningfully.
Does everyone respond the same way?
No. Glucose responses to the same food vary substantially between people, and net carbs is an approximation of a response rather than a measurement of one.
Should I use this to manage diabetes?
Only with clinical guidance. Carbohydrate counting for diabetes is usually taught against total carbohydrate rather than net, and changing the basis without telling your care team can affect insulin dosing.
For a food's effect adjusted for portion, see the glycemic load calculator. For daily fibre targets, see the fiber intake calculator.