To get net carbs, you subtract fiber and sugar alcohols from the total carbohydrates listed on a nutrition label. If a food has 24 grams of total carbs, 10 grams of fiber, and 8 grams of sugar alcohols, its net carbs would be 6 grams. The idea behind this calculation is simple: not all carbohydrates raise your blood sugar the same way, so net carbs tries to capture only the ones that do.
The Basic Formula
The standard calculation looks like this:
- Net Carbs = Total Carbohydrates − Fiber − Sugar Alcohols
Total carbohydrates on a U.S. nutrition label include everything: starches, sugars, fiber, and sugar alcohols. Fiber passes through your digestive system largely undigested, so it doesn’t spike blood sugar the way starch or table sugar does. Sugar alcohols (ingredients like erythritol, xylitol, sorbitol, and maltitol found in many “sugar-free” products) also have a reduced effect on blood sugar compared to regular sugar, which is why they get subtracted too.
For whole foods without a label, such as vegetables or nuts, the same math applies. Look up the total carbohydrates and fiber content, then subtract. An avocado, for instance, has about 12 grams of total carbs and 10 grams of fiber, leaving roughly 2 grams of net carbs.
Why “Net Carbs” Isn’t on the Label
You won’t find “net carbs” printed on any official nutrition facts panel in the United States. The FDA does not define or regulate the term. Federal labeling rules require manufacturers to list total carbohydrates and break them into dietary fiber, total sugars, added sugars, and sugar alcohols, but the agency has never created a legal standard for “net carbs.” That means when a product’s packaging advertises a net carb count, the company calculated it using whatever method it chose. Most use the standard subtraction formula, but there’s no regulatory body verifying the number.
Not All Sugar Alcohols Are Equal
The formula treats all sugar alcohols as if they have zero impact on blood sugar, but that’s an oversimplification. Erythritol has virtually no glycemic effect and is nearly calorie-free. Maltitol, on the other hand, raises blood sugar about 75% as much as regular sugar. If you’re tracking net carbs to manage blood sugar or stay in ketosis, a product sweetened with maltitol will hit harder than the net carb number suggests.
Some people who track carbs carefully count only half the grams of sugar alcohols (other than erythritol) rather than subtracting them entirely. This gives a more conservative estimate. If a protein bar lists 15 grams of sugar alcohols from maltitol, subtracting only 7 or 8 grams instead of all 15 may better reflect what your body actually experiences.
Allulose Gets Special Treatment
Allulose is a rare sugar that’s increasingly common in low-carb products. It tastes like sugar but provides only about 0.4 calories per gram (compared to 4 calories per gram for regular sugar) and has minimal effect on blood sugar. The FDA has issued guidance allowing manufacturers to exclude allulose from both the “Total Sugars” and “Added Sugars” lines on nutrition labels. However, allulose is still included in the total carbohydrate count, which means you may need to subtract it yourself when calculating net carbs. Check the ingredients list. If allulose is listed, look for its gram amount on the label and subtract it along with fiber and sugar alcohols.
The Fiber Subtraction Isn’t Perfect Either
The formula assumes fiber contributes zero usable energy, but that’s not entirely accurate. Insoluble fiber (the kind in wheat bran and vegetable skins) passes through your system mostly intact and genuinely contributes no calories. Soluble fiber (found in oats, beans, and some fruits) dissolves in water, gets fermented by bacteria in your large intestine, and does provide some calories, roughly 2 per gram compared to 4 per gram for starch or sugar. Soluble fiber still slows digestion and helps prevent rapid blood sugar spikes, so subtracting it makes sense for blood sugar purposes. But it’s worth knowing that “zero net carbs” doesn’t always mean zero caloric impact.
Whole Foods vs. Packaged “Keto” Products
This is where net carb math gets messy in practice. The fiber in broccoli, avocados, and almonds behaves predictably. You can subtract it with confidence, and most people tracking carbs for ketosis or blood sugar management do fine with these foods. Packaged products marketed as low-carb or keto are a different story.
Many keto breads, tortillas, protein bars, and ice creams use modified starches or added functional fibers to push down their net carb count on paper. In practice, these ingredients don’t always behave like the fiber in whole foods. A common experience among people following ketogenic diets is that a “3 net carb” tortilla made with modified wheat starch knocks them out of ketosis, while eating the same number of net carbs from vegetables doesn’t. Some of this is individual variation, but the pattern is consistent enough that it’s worth paying attention to.
Ingredients like maltodextrin are another red flag. It’s a processed starch that spikes blood sugar more aggressively than table sugar, yet it can appear in products that look low-carb based on the label. If a food’s net carb count seems too good to be true given its taste and ingredients, your body may respond to it as if the carbs are higher than advertised.
Reading Labels Outside the U.S.
If you’re looking at a product made in the UK, EU, or Australia, the carbohydrate number on the label typically already excludes fiber. These countries list fiber as a separate line item that isn’t rolled into total carbohydrates. That means subtracting fiber again would give you an artificially low number. For imported products or international nutrition databases, check whether the carbohydrate figure already accounts for fiber before doing any math.
A Practical Approach
For most people, the simple formula (total carbs minus fiber minus sugar alcohols) works well enough with whole, minimally processed foods. Where it gets unreliable is with heavily engineered packaged products. If you’re using net carbs to manage a health condition like diabetes or to maintain ketosis, a few practical habits help:
- Check which sugar alcohol is used. Erythritol can be fully subtracted. Maltitol and sorbitol deserve a half-subtraction at most.
- Look for allulose in the ingredients. Subtract it from total carbs if the label hasn’t already.
- Be skeptical of processed “low net carb” foods. If a bread has 15 grams of total carbs and claims 2 net carbs, test how your body actually responds before relying on that number.
- Don’t subtract fiber twice on international labels. Verify whether the total carbohydrate figure already excludes it.
Net carbs is a useful shorthand, not a precise metabolic measurement. It works best as a general guide, especially when you’re eating real food and paying attention to how your body responds rather than trusting the math alone.