Net carbs are the number that actually matters on keto, and they are not the number on the front of the package. This calculator takes the total carbohydrate, the fiber, and any sugar alcohols from a nutrition label and returns the net carbs your body really counts, using the rule that fiber and certain sugar alcohols do not raise blood sugar the way digestible carbs do.
The catch most calculators get wrong is sugar alcohols. They are not all equal: erythritol and allulose pass through with almost no blood-sugar effect, so they come out in full, while maltitol and most other polyols are partly absorbed and only count for about half. Pick the type from the menu and the math adjusts, instead of pretending every sweetener behaves the same.
How it works
Net carbs start from the total carbohydrate on the label, not the sugars line. Total carbohydrate already includes fiber and sugar alcohols, so the job is to subtract back out the parts that do not digest into glucose.
Fiber is subtracted in full. Your body does not break dietary fiber into glucose, so it does not count toward net carbs.
Erythritol and allulose are subtracted in full. Both leave the body almost unchanged, with a glycemic index near zero. Allulose is excluded from total sugars on US labels by FDA guidance.
Maltitol and most other sugar alcohols (xylitol, sorbitol, isomalt) are subtracted at half. They are partly absorbed and do raise blood sugar somewhat, with maltitol around a glycemic index of 35, so half is the standard keto adjustment.
Sugars are never subtracted. They are digestible carbs and already inside the total.
This follows the common US keto convention. In the EU and much of the rest of the world, the carbohydrate value on a label already excludes fiber, so net carbs there usually just means subtract the sugar alcohols. The calculator assumes a US label.
Frequently asked questions
Why are sugar alcohols not subtracted in full?
Because most of them are partly digested. Erythritol and allulose pass through almost untouched, so they come out completely. Maltitol, xylitol, and sorbitol are absorbed enough to raise blood sugar, so the standard keto rule counts only half of their grams.
What is the difference between US and EU net carbs?
It is where fiber sits. On a US label, fiber is inside the total carbohydrate, so you subtract it yourself. On an EU label, the carbohydrate value already excludes fiber, so the number is closer to net carbs before you start. This tool assumes a US label.
Should I subtract sugars too?
No. Sugars are fully digestible carbohydrate and are already part of the total. Only fiber and qualifying sugar alcohols come out. Subtracting sugar would undercount your carbs.
Why does my result differ from the package net carb claim?
Many brands subtract all sugar alcohols in full to print a smaller number, even maltitol. This tool only does that for erythritol and allulose and halves the rest, so it can read higher than the box. The higher number is the safer one to trust.
Do I count net carbs or total carbs on keto?
Most people on keto track net carbs, since fiber and erythritol do not affect blood sugar. If you are diabetic or following medical advice to watch total carbs, count total instead. See the note below.
This calculator is for general education, not medical or nutritional advice. Net carb counting is a dietary convention, not a clinical standard, and individual responses to fiber and sugar alcohols vary. If you have diabetes or another medical condition, follow the carbohydrate guidance your healthcare provider gives you, which may be based on total carbs.