Net Carbs Calculator
Calculate net carbs by subtracting fiber and half of sugar alcohols from total carbohydrates.
Results
Visualization
How It Works
Net carbs represent the carbohydrates that your body can actually digest and convert to glucose. Fiber passes through undigested and sugar alcohols are only partially absorbed, so both are subtracted from total carbs to give a more accurate picture of blood sugar impact.
The Formula
Variables
- Total_Carbs — All carbohydrates listed on the nutrition label in grams
- Fiber — Dietary fiber, which is indigestible and does not raise blood sugar
- Sugar_Alcohols — Sweeteners like erythritol, xylitol, maltitol - partially absorbed (50% average)
- Net_Carbs — Digestible carbohydrates that affect blood glucose and ketosis
Worked Example
A protein bar has 25 g total carbs, 8 g fiber, and 3 g sugar alcohols. Net carbs = 25 - 8 - (3/2) = 25 - 8 - 1.5 = 15.5 g. This bar would count as 15.5 g toward your daily keto carb limit.
Practical Tips
- Erythritol has a glycemic index of zero and can be fully subtracted (not just 50%) - it is the exception among sugar alcohols.
- Maltitol has a higher glycemic impact than other sugar alcohols and some keto dieters subtract only 25% instead of 50%.
- On US nutrition labels, fiber is already included in total carbs. On many European labels it is listed separately and should not be subtracted again.
- Aim for 20-25 g net carbs per day when starting keto; you can test higher limits (up to 50 g) once fat-adapted.
- Whole food sources of carbs (vegetables, nuts) have better fiber-to-carb ratios than processed low-carb products.
Frequently Asked Questions
Why do we only subtract half of sugar alcohols?
Sugar alcohols vary in how much they are absorbed. Erythritol is barely absorbed (0 net impact), while maltitol is about 75% absorbed. The 50% rule is a practical average. For precise tracking, research the specific sugar alcohol used.
Do net carbs matter for non-keto diets?
Net carbs are most relevant for keto and very low-carb diets where small differences matter for ketosis. For general health, total carb quality (whole grains vs refined) matters more than the exact net carb count.
Can I eat unlimited fiber and stay in ketosis?
Technically, since fiber does not raise blood sugar, high-fiber foods with low net carbs are keto-friendly. However, very high fiber intake can cause digestive discomfort. Focus on nutrient-dense fiber sources like vegetables and seeds.
Are net carbs listed on nutrition labels?
Not on standard US FDA nutrition labels, which show total carbs with fiber and sugars as sub-items. You must calculate net carbs yourself. Some keto-marketed products voluntarily list net carbs, but verify their math.
Do sugar-free products always have low net carbs?
Not necessarily. Sugar-free products may replace sugar with maltodextrin or other high-glycemic fillers that count fully as net carbs. Always check the full ingredient list and total carbohydrate content, not just the sugar-free claim.