To get net carbs, you subtract fiber and sugar alcohols from the total carbohydrates listed on a nutrition label. The basic formula is: total carbs minus fiber minus sugar alcohols equals net carbs. But the details matter, because not all sugar alcohols are treated equally, and where you live changes whether you need to do this math at all.
The Basic Net Carbs Formula
Net carbs represent the carbohydrates your body actually digests and converts to glucose. Fiber passes through your digestive system without being absorbed, so it doesn’t raise blood sugar despite being counted under total carbohydrates on U.S. nutrition labels. That’s why you subtract it.
For a food with 25 grams of total carbs and 7 grams of fiber, the net carbs would be 18 grams. If the product also contains sugar alcohols, you subtract those too, but with an important caveat covered below.
Why Sugar Alcohols Need a Different Approach
Sugar alcohols (listed on labels as erythritol, xylitol, maltitol, sorbitol, and others) are partially absorbed by your body. They have a smaller effect on blood sugar than regular sugar, but most of them aren’t completely ignored by your metabolism either.
The UCSF Diabetes Teaching Center recommends subtracting only half the grams of sugar alcohol from total carbohydrates. So if a protein bar lists 20 grams of total carbs, 4 grams of fiber, and 18 grams of sugar alcohols, the math works like this: divide the sugar alcohols in half (18 ÷ 2 = 9), then subtract both the fiber and that halved number from total carbs (20 − 4 − 9 = 7 net carbs).
Erythritol is the one common exception. It has virtually no caloric impact and doesn’t raise blood sugar, so many people following keto or low-carb diets subtract erythritol fully rather than using the half rule. If a label breaks out erythritol separately, you can reasonably subtract 100% of it.
Where Allulose Fits In
Allulose is a newer sweetener showing up in low-carb products. It’s technically a sugar, but your body absorbs very little of it. The FDA has issued guidance allowing manufacturers to exclude allulose from “Total Sugars” and “Added Sugars” on nutrition labels, and a citizen petition has requested its exclusion from “Total Carbohydrate” as well.
In practice, some products still include allulose in total carbs while others don’t. Check the ingredient list and the label’s footnotes. If allulose is included in the total carbohydrate count, you can subtract it when calculating net carbs, since its caloric contribution is minimal (roughly 0.4 calories per gram, compared to 4 calories per gram for regular sugar).
If You’re Reading a European Label, Stop Subtracting
This entire calculation assumes you’re looking at a U.S. or Canadian nutrition label. In the United States and Canada, total carbohydrates are calculated by a method called “carbohydrate by subtraction,” where everything that isn’t protein, fat, water, or ash gets lumped into the carb number. That means fiber is already baked into the total.
In the EU and Mexico, labels use “available carbohydrate,” which only counts sugars and starches. Fiber is already excluded from the carbohydrate line. So if you’re reading a European food label, the carbohydrate number is essentially net carbs already. Subtracting fiber again would give you an artificially low number.
A Quick Reference for Common Scenarios
- Food with fiber only: Total carbs minus fiber = net carbs
- Food with fiber and sugar alcohols: Total carbs minus fiber minus half the sugar alcohols = net carbs
- Food with erythritol specifically: Total carbs minus fiber minus all erythritol = net carbs
- Food with allulose in the carb count: Total carbs minus fiber minus allulose = net carbs
- EU or Mexican label: The carbohydrate number already excludes fiber, so no subtraction is needed
Why “Net Carbs” Isn’t on the Label
The FDA doesn’t regulate or define the term “net carbs.” You won’t find it on a standard Nutrition Facts panel because it’s not an official measurement. When food companies print net carbs on their packaging, they’re using their own calculations, and those methods aren’t always consistent. Some brands subtract all sugar alcohols fully. Others use the half rule. Some subtract allulose, others don’t list it separately at all.
This is why knowing the formula yourself matters more than trusting the front-of-package marketing. Flip to the Nutrition Facts panel, find total carbohydrates, look for dietary fiber and sugar alcohols listed underneath, and do the subtraction. It takes ten seconds once you know what to look for, and you’ll get a more reliable number than whatever a brand decided to print in large font on the front of the bag.