Net Carbs Calculator
Enter the total carbohydrates, fiber, and any sugar alcohols from a nutrition label to calculate net carbs - the carbohydrates that actually impact your blood sugar. The calculator accounts for different sugar alcohol types with their correct absorption factors, so your count is accurate whether you are tracking for keto, low-carb, or general health.
What are net carbs?
Net carbs - sometimes called digestible carbs or impact carbs - are the portion of total carbohydrates that your body can break down and absorb as glucose. Dietary fiber and most sugar alcohols pass through the digestive system with little or no impact on blood sugar, so they are subtracted from the total carbohydrate figure. The result is the number that actually matters for blood glucose management, insulin response, and low-carb tracking. For whole, unprocessed foods the formula is straightforward: net carbs = total carbs - fiber. For packaged foods that contain sugar alcohols, you also subtract the absorbed portion of those sweeteners.
How to read a nutrition label for net carbs
In the United States and Canada, the Nutrition Facts panel lists "Total Carbohydrate" and shows fiber and sugars as indented sub-items. Fiber is already included in the total, so you subtract it. Sugar alcohols may appear as another sub-item; subtract half their grams unless the only sugar alcohol is erythritol, in which case you subtract all of it. In Australia and most of Europe, labels display carbohydrates excluding fiber by default, so no fiber subtraction is needed - just handle any sugar alcohols as described. This calculator includes a region selector so the right arithmetic is applied automatically.
Why sugar alcohol type matters
Not all sugar alcohols behave the same way. Erythritol has a glycemic index of essentially zero because roughly 90% of it is absorbed into the bloodstream early and then excreted in urine intact, never reaching the colon and never spiking blood sugar. Xylitol, sorbitol, isomalt and lactitol have glycemic indices in the single digits and are only partially absorbed, so half their carb grams are the standard conservative deduction. Maltitol has a higher glycemic index of about 35 - closer to table sugar than the other polyols - so it contributes more to blood sugar than the 50% rule implies. If your product contains mainly maltitol and you have diabetes or are in strict ketosis, treat those grams more carefully.
Net carbs on a keto or low-carb diet
A typical ketogenic diet targets 20 to 50 grams of net carbs per day to maintain nutritional ketosis. A standard low-carb diet may allow 50 to 100 grams. Knowing the net carb count for each food you eat makes it easier to stay within your target without obsessing over vegetables and whole foods that are high in fiber. An avocado, for example, has about 17 g total carbs but only 3 to 4 g net carbs because most of those carbs are fiber. High-fiber choices like leafy greens, broccoli, and nuts are similarly favorable on a net-carb basis. The percent-of-budget output in this calculator lets you see at a glance how a food fits into a 50 g daily limit.
Sugar alcohol absorption factors
| Sugar alcohol | Glycemic index | Absorption factor | Net carb impact |
|---|---|---|---|
| Erythritol | 0 | 0 (subtract all) | None |
| Mannitol | ~0 | 0.5 (subtract half) | Low |
| Isomalt | 9 | 0.5 (subtract half) | Low |
| Sorbitol | 9 | 0.5 (subtract half) | Low |
| Xylitol | 13 | 0.5 (subtract half) | Low |
| Lactitol | 6 | 0.5 (subtract half) | Low |
| Maltitol | 35 | 0.5 (subtract half) | Moderate |
| Mixed / unknown | - | 0.5 (conservative) | Varies |
The factor shown is the fraction of sugar alcohol carbs that count toward net carbs. Erythritol is excreted in urine and has a glycemic index of 0, so all of it is subtracted.
Frequently asked questions
What is the net carbs formula?
For whole foods: Net carbs = Total carbohydrates - Fiber. For processed foods with sugar alcohols: Net carbs = Total carbohydrates - Fiber - (Sugar alcohols x absorption factor). The absorption factor is 0 for erythritol (subtract all) and 0.5 for most other sugar alcohols (subtract half). This calculator applies the correct factor automatically based on the sugar alcohol type you select.
Should I subtract all sugar alcohols or just half?
It depends on the type. Erythritol is excreted in urine without raising blood sugar, so its grams are fully subtracted. All other common sugar alcohols - xylitol, sorbitol, isomalt, lactitol, mannitol and maltitol - are only partially absorbed, so the conservative approach is to subtract half. Maltitol has a relatively high glycemic index of about 35, so some practitioners subtract less than half for that one. If the label lists "sugar alcohols" without specifying the type, the standard advice is to subtract half.
Do I subtract fiber on every nutrition label?
Only if you are reading a US or Canadian label, where fiber is included inside the Total Carbohydrate figure. Australian and European labels already exclude fiber from the carbohydrate total, so subtracting it again would double-count the deduction. Use the region selector in this calculator to apply the right method automatically.
Are net carbs the same as glycemic carbs?
Net carbs and glycemic carbs are similar but not identical. Net carbs is an operational shorthand that uses total carbs minus fiber and sugar alcohols. Glycemic carbs technically refers only to carbohydrates that measurably raise blood glucose, which can differ slightly depending on individual gut bacteria and how soluble fiber is fermented. For practical tracking purposes, net carbs is the standard term used on keto and low-carb plans.
How many net carbs per day for keto?
Most ketogenic protocols target between 20 and 50 grams of net carbs per day. Stricter approaches use 20 g to ensure most people enter ketosis. Moderate low-carb diets extend the range to 50 to 100 g. The right amount varies by body weight, activity level and individual metabolic response. The keto-budget gauge in this calculator is calibrated to the 50 g benchmark, which is a common moderate keto ceiling.
Does fiber count as a carb on a keto diet?
No. Dietary fiber is technically a carbohydrate but the human body lacks the enzymes to break it down into glucose. Insoluble fiber passes through the gut unchanged. Soluble fiber is fermented by gut bacteria into short-chain fatty acids, which provide a small amount of energy but do not spike blood glucose or insulin. Both types are subtracted when calculating net carbs, making high-fiber foods like avocado, leafy greens, chia seeds and broccoli much more keto-friendly than their total carb count suggests.