What Can You Deduct From Carbs to Calculate Net Carbs?

December 10, 2025 •

3 min read

The term "net carbs" is not legally defined by the Food and Drug Administration, yet it is widely used in low-carb diets. This practice involves a calculation to determine how many carbohydrates your body actually absorbs, but it is important to understand what you can deduct from carbs to get an accurate number.

Quick Summary

Net carbs are calculated by subtracting grams of fiber and, in some cases, sugar alcohols from total carbohydrates. This practice, popular with low-carb diets, helps estimate the carbohydrates that affect blood sugar, but there is no official consensus or regulatory standard.

Key Points

Fiber Deduction: To calculate net carbs, you can deduct the total grams of dietary fiber from the total carbohydrate count.
Sugar Alcohol Deduction: For packaged goods, a portion of sugar alcohols, typically half, can be deducted from total carbs, though some types like erythritol can be fully subtracted.
No Legal Definition: The term "net carbs" is not regulated or recognized by the FDA, meaning there is no official standard for its calculation.
Inaccurate for Processed Foods: Calculating net carbs for processed items can be unreliable due to varying digestibility of added fibers and sugar alcohols.
Prioritize Total Carbs for Health: Health professionals often recommend using the total carbohydrate count, especially for diabetes management, to avoid potential blood sugar spikes from partially digested carbs.

Understanding Total vs. Net Carbs

Nutrition labels list 'Total Carbohydrate,' which includes starches, sugars, dietary fiber, and sugar alcohols. However, the body doesn't digest all of these the same way. Net carbs represent the digestible carbohydrates that are converted to glucose for energy. Fiber and most sugar alcohols are not fully digested, which is why they are often subtracted in low-carb diets like keto.

What Exactly Do You Deduct?

To calculate net carbs, you primarily subtract dietary fiber and sugar alcohols from total carbohydrates.

Dietary Fiber: Fiber is a complex carbohydrate that isn't broken down into sugar. You typically subtract the full amount of dietary fiber listed.
Sugar Alcohols: These sweeteners are partially digested and affect blood sugar differently. A common approach is to subtract half the grams of most sugar alcohols. Erythritol, which isn't absorbed, can often be fully subtracted. The calculation for products with sugar alcohols can be imprecise due to variations in digestion and labeling.

How to Calculate Net Carbs Step-by-Step

To calculate net carbs using a nutrition label, subtract the total grams of 'Dietary Fiber' from 'Total Carbohydrate'. If 'Sugar Alcohols' are listed, subtract a portion (often half, but potentially all for erythritol). The result is the estimated net carbs.

Comparison of Net Carb Formulas

Different approaches exist for calculating net carbs, especially regarding fiber and sugar alcohols, and regional labeling laws vary.


Feature	U.S. Standard Practice	Ketogenic Diet Practice	European/UK Standard
Basis	Total Carbs - Fiber - Half Sugar Alcohols	Total Carbs - Fiber - All Erythritol (or similar formula).	Total Carbs - Polyols (Sugar Alcohols).
Fiber Deduction	Full deduction.	Full deduction.	Fiber is already excluded from 'Total Carbs'.
Sugar Alcohol Deduction	Generally half; full for erythritol.	Often more aggressive.	Polyols listed and fully subtracted.
Regulatory Status	Not legally defined by FDA.	Based on dietary practice.	Reflects regional labeling laws.
Accuracy	Varies by sugar alcohol type.	Seen as inaccurate by health professionals.	More straightforward due to labeling differences.

Controversy and Considerations

The concept of net carbs is debated and not recognized by organizations like the American Diabetes Association (ADA), which advises using total carbohydrates. Some concerns involve fiber and sugar alcohols still potentially impacting blood glucose and the variability of digestion.

Marketing Tactic: Some sources view "net carbs" as a marketing strategy for processed foods that could lead to unexpected blood sugar spikes.
Individual Variation: Responses to fiber and sugar alcohols differ among individuals, affecting the reliability of a single calculation. Monitoring blood glucose is advised for those with diabetes.
Whole vs. Processed Foods: The net carb concept is more relevant for whole foods with natural fiber. For processed foods with added fibers and sugar alcohols, the calculation may be less dependable.

Focusing on whole, high-fiber foods is generally more important than precise net carb calculations for healthy eating. The net carb method can be a useful tool, but exercising caution with processed items is recommended.

Conclusion: A Calculated Approach to Carbs

Calculating net carbs by deducting fiber and sugar alcohols is a common practice in low-carb diets but lacks official regulation and is debated by health professionals. Using total carbohydrates and observing individual blood sugar responses is often considered more reliable, especially for diabetes management. Prioritizing whole, unprocessed foods with natural fiber is a healthier overall strategy. For further information on carbohydrate counting for diabetes, resources are available from the UC San Francisco Diabetes Teaching Center.

What can you deduct from carbs?: Key Takeaways

Subtract Fiber: To calculate net carbs, deduct the total dietary fiber from total carbohydrates.
Deduct Sugar Alcohols: Subtract half of most sugar alcohols, but potentially all for erythritol.
Net Carbs are Unregulated: The FDA and ADA do not officially recognize or define "net carbs".
Accuracy Varies: Net carb calculations can be less accurate for processed foods due to variations in digestibility.
Focus on Whole Foods: Prioritize whole foods with natural fiber over relying solely on net carb counts for processed items.

Frequently Asked Questions

To calculate net carbs, you subtract the total grams of dietary fiber and a portion of any sugar alcohols from the total grams of carbohydrates listed on a food's nutrition label.

The reliability of net carb calculations is debated. The term is not legally defined, and different types of fiber and sugar alcohols can have varying effects on blood sugar, which a simple calculation may not accurately reflect.

Most sugar alcohols are only partially digested by the body, so they still contribute some calories and can impact blood sugar. For this reason, a common practice is to subtract only half of the grams.

Total carbs include all types of carbohydrates in a food, including sugars, fiber, and sugar alcohols. Net carbs are the estimate of only the digestible carbs that the body absorbs and uses for energy.

For a ketogenic diet, many people count net carbs to monitor their intake of carbohydrates that affect blood sugar. This allows them to consume certain high-fiber foods that have a lower net carb impact.

The American Diabetes Association (ADA) does not recognize or recommend counting net carbs. Instead, the ADA advises using total carbohydrates on nutrition labels for managing diabetes and monitoring how foods affect blood glucose.

For weight loss, focusing on whole foods high in fiber is generally more effective than relying on potentially inaccurate net carb counts, especially with processed foods. Total carbohydrates can be a more straightforward metric to track.