Net carbs equal the total carbohydrates in a food minus the fiber and any sugar alcohols. This simple subtraction gives you a rough estimate of the carbohydrates your body actually absorbs and uses for energy. The concept isn’t an official FDA measurement, but it’s widely used by people following low-carb and ketogenic diets to track their daily intake.
The Basic Formula
Start with the total carbohydrates listed on the nutrition label. Subtract the grams of dietary fiber. If the product contains sugar alcohols, subtract those too. What’s left is your net carb count.
Net Carbs = Total Carbohydrates − Fiber − Sugar Alcohols
For example, if a protein bar has 24 grams of total carbs, 8 grams of fiber, and 10 grams of sugar alcohols, the net carb count is 6 grams. Fiber and sugar alcohols get subtracted because they pass through your digestive system without significantly raising blood sugar. Fiber is either fermented by gut bacteria or excreted, and sugar alcohols are only partially absorbed.
Why Fiber Gets Subtracted
Dietary fiber is technically a carbohydrate, so it’s included in the total carb count on every nutrition label. But your body can’t break it down into glucose the way it handles starches and sugars. Some fiber is fermented by bacteria in your large intestine, producing small amounts of energy, while insoluble fiber passes through entirely unchanged. Either way, the blood sugar impact is minimal.
The FDA’s definition of dietary fiber covers both the fiber naturally present in plants and certain added fibers that have demonstrated health benefits. These include ingredients like inulin, psyllium husk, beta-glucan, pectin, guar gum, and cellulose, among others. If you see any of these on an ingredient list, they’re already counted in the fiber line on the nutrition panel, so you don’t need to do anything extra.
How Sugar Alcohols Factor In
Sugar alcohols are sweeteners commonly found in “sugar-free” or “low-carb” products like candy bars, protein bars, and ice cream. They taste sweet but are only partially digested, so they contribute fewer calories and less blood sugar impact than regular sugar. The most common ones you’ll see on ingredient lists are erythritol, xylitol, sorbitol, maltitol, isomalt, mannitol, and lactitol.
Not all sugar alcohols behave the same way, though. Erythritol is almost entirely excreted without being metabolized, contributing essentially zero usable carbs. Maltitol, on the other hand, is absorbed more readily and can raise blood sugar noticeably. Some people subtract only half the sugar alcohol grams when the product contains maltitol or sorbitol, keeping the full subtraction only for erythritol. This isn’t an official standard, but it gives a more conservative estimate if you’re closely managing blood sugar.
Sugar alcohols aren’t always broken out on the nutrition label. Manufacturers are only required to list them if the product makes a sugar-related claim like “sugar-free.” If you suspect a product contains sugar alcohols but don’t see them on the panel, scan the ingredient list for names ending in “-ol” or for hydrogenated starch hydrolysates (sometimes abbreviated HSH).
The Allulose Exception
Allulose is a rare sugar that’s become popular in low-carb products, and it creates a labeling quirk worth knowing about. Your body absorbs allulose quickly but doesn’t metabolize it. About 70% of what you eat is eliminated intact in urine and feces within 48 hours, and it provides no more than 0.4 calories per gram (compared to 4 calories per gram for regular sugar). It produces a negligible blood sugar response.
Here’s the catch: the FDA currently requires allulose to be included in the total carbohydrate number on the label, even though it acts nothing like a typical carb. However, the FDA allows manufacturers to exclude it from both the “Total Sugars” and “Added Sugars” lines. This means a product sweetened with allulose may show a surprisingly high total carb number while listing very few sugars. To get accurate net carbs, you’ll need to check the ingredient list for allulose, find its gram amount (some brands list it separately on the panel or in marketing materials), and subtract it along with fiber and sugar alcohols.
Reading a U.S. Nutrition Label Step by Step
Pull up any packaged food and look at the Nutrition Facts panel. Here’s what to do:
- Find Total Carbohydrate. This is your starting number. It includes everything: starch, sugar, fiber, sugar alcohols, and allulose.
- Subtract Dietary Fiber. This line is indented under Total Carbohydrate. Subtract all of it.
- Subtract Sugar Alcohols (if listed). Also indented under Total Carbohydrate when present. Subtract the full amount for erythritol. Consider subtracting only half for maltitol or sorbitol if you want a conservative estimate.
- Check the ingredient list for allulose. If it’s there but not broken out on the panel, you may need to look at the brand’s website or packaging claims for the gram amount.
If you’re outside the U.S., labels in the UK, EU, and Australia already list “Carbohydrate” as net carbs by default. Fiber is reported on a separate line and isn’t included in the carb total. In those countries, you don’t need to subtract anything.
Net Carbs in Whole Foods
Whole foods don’t come with nutrition panels, so you’ll need a reference or app. The calculation is the same: total carbs minus fiber. Here are some common examples per one-cup serving to give you a feel for how fiber changes the picture:
- Avocado (chopped): 13 g total carbs, 10 g fiber = 3 g net carbs
- Spinach (cooked): 7 g total carbs, 4 g fiber = 3 g net carbs
- Asparagus (cooked): 7 g total carbs, 4 g fiber = 3 g net carbs
- Broccoli (raw): 6 g total carbs, 2 g fiber = 4 g net carbs
- Cauliflower (raw): 5 g total carbs, 2 g fiber = 3 g net carbs
- Zucchini (raw): 4 g total carbs, 1 g fiber = 3 g net carbs
- Mushrooms (raw): 2 g total carbs, 1 g fiber = 1 g net carb
- Bell pepper (red, chopped): 9 g total carbs, 3 g fiber = 6 g net carbs
- Green beans (cooked): 10 g total carbs, 4 g fiber = 6 g net carbs
Avocado stands out: nearly 77% of its carbohydrate content is fiber, leaving just 3 grams of net carbs per cup. Most non-starchy vegetables land between 1 and 6 net carbs per cup, which is why they’re staples on low-carb diets even though their total carb numbers might look moderate at first glance.
Common Mistakes to Avoid
The biggest error people make is double-subtracting. If a label already shows a low carb number and also lists fiber separately, check whether the label is using international formatting (where fiber is already excluded). Subtracting fiber again would undercount your carbs.
Another common mistake is treating all sugar alcohols as zero-impact. Maltitol, in particular, has a glycemic index around 35, which is lower than table sugar’s 65 but far from zero. If you’re tracking net carbs to manage blood sugar rather than just for general low-carb eating, paying attention to which sugar alcohol is in a product matters.
Finally, be cautious with products that market a very low net carb number on the front of the package. Some brands use creative combinations of fiber additives, sugar alcohols, and allulose to engineer an impressively low number. The math may technically check out, but your body’s response to a bar with 20 grams of maltitol will be different from one with 20 grams of erythritol. When the net carb claim seems too good to be true, flip the package over and look at what’s actually in it.