"Net carbs" shows up constantly on keto and low-carb recipes, but it's not a number that appears on an official nutrition label — it's a calculated figure, and knowing the calculation matters if you're actually tracking it.
The formula
Net carbs = total carbohydrates − fiber (and, in some calculations, minus sugar alcohols too, if the recipe includes them). The logic behind subtracting fiber is that fiber, while technically a carbohydrate, isn't broken down and absorbed by the body the same way starches and sugars are — it passes through largely intact, so it doesn't raise blood sugar the way other carbs do.
Why this distinction exists
Total carbohydrate counts include fiber, starches, and sugars all together. For general nutrition tracking, that combined number is fine. For low-carb and keto approaches specifically, where the goal is often managing blood sugar response, fiber's different metabolic behavior means it makes sense to separate it out — a food high in fiber but otherwise low in starch/sugar can have a very different practical effect than its total-carb number alone suggests.
A concrete example
A serving with 10g total carbohydrates and 6g of that from fiber has a net carb count of 4g, not 10g. That's a meaningful difference for anyone tracking a specific daily net-carb target, which is exactly why high-fiber, low-starch vegetables (like leafy greens or zucchini) are staples in keto cooking — their total carbs look higher than their net-carb impact actually is.
Where it gets debated
Not every source calculates net carbs identically — some subtract only fiber, others subtract fiber and sugar alcohols (common in recipes using sugar substitutes like erythritol). This isn't a settled, universally standardized figure the way total carbohydrate is, which is worth knowing if you're comparing net-carb numbers across different recipes or sources — they may not be using the exact same formula.
The practical takeaway
If you're tracking net carbs, total carbohydrates and fiber (both usually shown on a standard nutrition breakdown) are the two numbers you actually need — net carbs is just simple subtraction from there, not a separate measurement.