Calculate net carbs by subtracting fiber and sugar alcohols from total carbohydrates. Essential for keto, low-carb, and diabetic diets.
Net carbs represent the carbohydrates that your body actually digests and converts to glucose, impacting blood sugar and insulin levels. The concept is straightforward: take total carbohydrates and subtract fiber (which passes through undigested) and a portion of sugar alcohols (which are only partially absorbed).
This distinction matters enormously for anyone following a ketogenic diet (typically 20–50g net carbs), a low-carb diet, or managing blood sugar. A food with 30g total carbs but 15g of fiber has only 15g net carbs — a very different metabolic impact.
Sugar alcohols (erythritol, xylitol, maltitol, sorbitol, etc.) add complexity because each has a different absorption rate. Erythritol has virtually zero glycemic impact and can be fully subtracted, while maltitol is absorbed at ~50% and should only be half-subtracted. This calculator handles all common sugar alcohols with their correct absorption rates. Whether you are a beginner or experienced professional, this free online tool provides instant, reliable results without manual computation.
If you're counting carbs for keto or blood sugar management, using total carbs overestimates the metabolic impact. Net carbs give a more accurate picture of how a food will actually affect your blood glucose and ketosis. This calculator handles the tricky sugar alcohol math that many people get wrong, ensuring you stay on target.
Net Carbs = Total Carbs – Fiber – (Sugar Alcohols × Absorption Factor) Sugar Alcohol Absorption Factors: • Erythritol: 0% absorbed (subtract 100%) • Xylitol: 50% absorbed (subtract 50%) • Sorbitol: 60% absorbed (subtract 40%) • Mannitol: 50% absorbed (subtract 50%) • Maltitol: 67% absorbed (subtract 33%) • Isomalt: 45% absorbed (subtract 55%) • Lactitol: 40% absorbed (subtract 60%) • Glycerin: 100% absorbed (subtract 0%) Fiber: 100% subtracted (insoluble) or nearly 100% (soluble contributes ~2 kcal/g but minimal glucose impact)
Result: 18g net carbs
Total carbs: 38g. Subtract fiber: 38 – 12 = 26g. Erythritol is 0% absorbed, so subtract fully: 26 – 8 = 18g net carbs. If the sugar alcohol were maltitol instead, only 33% would be subtracted: 38 – 12 – (8 × 0.33) = 23.4g net carbs — a significant difference for keto tracking.
Fiber passes through the stomach and small intestine largely intact. Insoluble fiber (cellulose, lignin) passes through completely undigested. Soluble fiber (pectin, beta-glucan, psyllium) is fermented by gut bacteria in the colon, producing short-chain fatty acids that provide approximately 2 kcal/g — but this energy comes from fatty acid metabolism, not glucose, so it doesn't meaningfully impact blood sugar or ketosis. This is why fiber is fully subtracted when calculating net carbs.
Sugar alcohols (polyols) are hydrogenated carbohydrates that taste sweet but are incompletely absorbed. They're found naturally in some fruits and fermented foods, and are widely used as sweeteners in "sugar-free" products.
Erythritol stands apart: it's absorbed in the small intestine (preventing GI distress) but not metabolized — it exits unchanged through the kidneys. This makes it effectively zero-calorie and zero-glycemic. Xylitol and sorbitol are partially absorbed and partially fermented, providing about 2.4 kcal/g (vs. 4 kcal/g for sugar). Maltitol is the most problematic for keto dieters because it has a glycemic index of 35–52 and provides about 3 kcal/g.
Avocado (100g): 9g total, 7g fiber = 2g net. Broccoli (1 cup): 6g total, 2.4g fiber = 3.6g net. Almonds (1 oz): 6g total, 3.5g fiber = 2.5g net. Raspberries (1 cup): 15g total, 8g fiber = 7g net. Cauliflower (1 cup): 5g total, 2g fiber = 3g net. Spinach (1 cup raw): 1g total, 0.7g fiber = 0.3g net.
Total carbs include everything classified as a carbohydrate: starches, sugars, fiber, and sugar alcohols. Net carbs include only the carbohydrates that raise blood sugar and provide usable glucose energy — essentially total carbs minus fiber and most sugar alcohols. For metabolic purposes (ketosis, blood sugar management), net carbs are more relevant than total carbs.
Most ketogenic diet guidelines use net carbs. The standard 20–50g daily carb limit for keto refers to net carbs. If you counted total carbs, you'd be unnecessarily restricting vegetables and other fiber-rich foods. However, some practitioners prefer total carbs for simplicity and a stricter approach. Either works if you're consistent.
Different sugar alcohols have different absorption rates in the small intestine. Erythritol is unique — it's absorbed but not metabolized, then excreted unchanged in urine, contributing ~0 kcal and zero glycemic impact. Other sugar alcohols like maltitol and sorbitol are partially fermented by gut bacteria or partially absorbed, providing some calories and some blood sugar impact.
Yes, potentially. Maltitol has a glycemic index of 35–52 (compared to sugar's 65), meaning it significantly raises blood sugar. Many "sugar-free" keto products use maltitol because it's cheap and sweet, but large amounts (20g+) can impair ketosis. Look for products using erythritol, stevia, or monk fruit instead — these have zero glycemic impact.
Less so, but it's still useful context. For general health, total carb quality matters more than the net/total distinction. However, understanding net carbs helps you recognize that high-fiber foods (vegetables, legumes, whole grains) have a lower glycemic impact than their total carb count suggests. This can help with satiety, blood sugar stability, and overall health.
US nutrition labels list total carbs with fiber as a sub-line. You must subtract fiber yourself. European/UK labels often list carbohydrates already minus fiber (as "available carbohydrates"), so the listed carbs are essentially already net carbs. If using European labels, do NOT subtract fiber again or you'll under-count. Always check what "carbohydrates" means on your label's country format.