Net Carbs — How to Calculate and Track Them
Ever wonder why two foods with the same total carbs behave differently on your blood sugar or keto meter? Net carbs explains that. It’s a simple way to estimate the carbs that actually affect your blood sugar, not a legal label or a magic number.
How to calculate net carbs
Most people use this basic formula: Net carbs = Total carbs − Fiber − Certain sugar alcohols. Look at the Nutrition Facts: take the total carbohydrates per serving, subtract fiber, then subtract sugar alcohols that don’t raise blood sugar much (like erythritol).
Example: a snack lists 20 g total carbs, 8 g fiber and 4 g erythritol. Net carbs = 20 − 8 − 4 = 8 g. Quick and useful.
Two important details: not all fibers and sugar alcohols act the same. Insoluble fiber is not absorbed and can be fully subtracted. Some soluble fibers (like inulin) ferment and may affect some people slightly. For sugar alcohols, erythritol is usually counted as zero; maltitol and sorbitol can raise blood sugar and are often counted partially or fully. If you want to be strict, subtract only fiber and erythritol; count other sugar alcohols as half or avoid them.
Practical tips & mistakes to avoid
Serving size matters. Labels can be sneaky: a pack may contain two servings. Always base net carbs on how much you actually eat. Want to stay under 20 g net carbs a day? Double-check servings before you snack.
"Net carbs" on a package is a marketing claim, not a regulated term in many countries. Don’t trust a big "0 net carbs" claim without checking the label. Some products subtract all sugar alcohols, which can understate impact.
If you’re using keto or blood-sugar goals, track for a week to see trends. Use a food app or a simple log: note total carbs, fiber, and any sugar alcohols. Compare how you feel and, if you use glucose monitoring, watch readings after meals. That tells you whether a product truly fits your plan.
Foods to rely on: non-starchy vegetables, leafy greens, avocados, eggs, fish, and most nuts have low net carbs. Berries are the best fruit option in small portions. Beware low-carb baked goods — they often use maltitol or large amounts of fiber that can upset digestion or affect blood sugar.
If you take diabetes meds or insulin, talk to your clinician before shifting carb targets. Net carbs are a tool, not a replacement for medical advice. For general low-carb or keto diets, a cautious approach is: subtract fiber and erythritol, treat other sugar alcohols as partial carbs, and always mind serving sizes.
Want a fast rule? Count total carbs minus fiber and erythritol. When in doubt, take the conservative route and count a bit more rather than less. That keeps your tracking honest and avoids surprise spikes.
