Understanding Net Carbs: How to Calculate Them Correctly
Total carbs, fiber, sugar alcohols, and net carbs — a plain-English explanation of the math that determines whether you stay in ketosis.
Medically reviewed by Elena Marsh · Certified Nutrition Coach (NASM-CNC)
Every article on Keto Kitchen Hub is fact-checked against peer-reviewed research and reviewed by a registered dietitian before publication. This content is for educational purposes and is not medical advice.
Ask ten keto followers how to calculate net carbs and you'll get ten slightly different answers. Here is the clearest, most widely accepted method — with the caveats you need to know.
The basic formula
Net carbs = Total carbohydrates − Dietary fiber − Sugar alcohols (specifically erythritol and allulose)
The logic: fiber is a carbohydrate your body largely cannot digest, so it passes through without meaningfully raising blood sugar or insulin. The same is true of certain sugar alcohols — erythritol is excreted almost entirely unchanged, and allulose is metabolized differently and does not spike glucose.
Why we subtract fiber
On a nutrition label, 'total carbohydrates' includes both digestible starch/sugar and indigestible fiber. Since fiber doesn't fuel your body or trigger an insulin response, subtracting it gives a better picture of the carbs that will actually affect your metabolism.
Sugar alcohols — the tricky part
- Erythritol — subtract fully; almost none is absorbed
- Allulose — subtract fully; metabolized differently from sugar
- Xylitol — subtract about half; partially absorbed and raises blood sugar mildly
- Maltitol — do not subtract; behaves nearly like sugar for many people
- Sorbitol — do not subtract; can spike glucose and cause GI issues
A worked example
A cup of raspberries: 15 g total carbs, 8 g fiber. Net carbs = 15 − 8 = 7 g.
A serving of keto brownies: 5 g total carbs, 3 g fiber, 15 g erythritol. Net carbs = 5 − 3 = 2 g.
The Australian / European difference
In Australia and much of Europe, nutrition labels list 'carbohydrates' with fiber already excluded. In that case, the number shown IS effectively net carbs — no subtraction needed. In the US, Canada, and most of Asia, fiber is included in total carbs and you must subtract.
How many net carbs should you eat?
Most people enter and maintain ketosis at 20–30 g net carbs per day. Athletes and lean, active individuals may tolerate 40–50 g.
The bottom line
Net carbs are a useful shortcut, not a magic number. Prioritize whole foods, be honest with your tracking for the first few weeks, and let your energy, cravings, and results tell you whether your intake is dialed in.
Frequently asked questions
Should I count carbs in vegetables?
Yes, but they're small. A cup of raw spinach is 0.4 g net; a cup of broccoli is 4 g. Track them but don't fear them.
What about fiber supplements?
Psyllium and inulin are subtracted like other fiber. Some people get GI upset from large doses — start small.
References
Dr. Julian Reyes, RD
Nutrition Reviewer · PhD Nutritional Sciences, Registered Dietitian
Julian reviews every article for scientific accuracy and appropriate scope. He researches metabolic health and lipid metabolism in academic and clinical settings.