Net Carbs vs. Total Carbs: The Only Formula You Need

What’s the net carbs formula?

Net carbs = Total carbs − Fiber

That’s it. That’s the whole formula. If a nutrition label lists 12g total carbs and 5g fiber, the net carb count is 7g.

Some trackers also subtract sugar alcohols (erythritol, xylitol, and similar), because the label’s total-carbohydrate line counts them in full. If a product lists sugar alcohols separately, the fuller formula is:

Net carbs = Total carbs − Fiber − Sugar alcohols

Many trackers subtract erythritol in full. Maltitol is the one exception worth knowing — some trackers subtract it only partially, or not at all. In TwentyGrams, maltitol falls under the “other” type and is deducted at 50%, the same as every sugar-alcohol type except erythritol and allulose.

In TwentyGrams specifically, this second step is automatic and fixed — not a setting anyone picks. Erythritol and allulose are deducted in full (100%); every other sugar-alcohol type (xylitol, sorbitol, maltitol, and so on, recorded as “other”) and any type marked “don’t know” is deducted at 50%. When a food lists sugar-alcohol grams but no type, a USDA Branded Foods item is deducted at 100%, matching the Net Carbs line that branded labels print, and an item from any other source is deducted at 50%. The rule is fixed and applied the same way for every user, every time — no protocol setting, no alternate protocol to choose between.

That deduction only shows up on a food once a sugar-alcohol figure has actually been recorded for it — either from the source data it was matched against, or a one-tap correction on that specific food. Most foods in the database currently show no sugar-alcohol deduction simply because nobody has entered a figure for that food yet, not because the food is free of sugar alcohols.

Non-nutritive sweeteners like stevia and monk fruit sit outside this formula entirely — they typically don’t add measurable carbs to the “Total Carbohydrate” line at all, so there’s nothing to subtract in the first place. That’s a different situation from sugar alcohols, which do show up in the total-carbs count and need to be subtracted back out.

Why does fiber get subtracted from total carbs?

Fiber passes through your digestive system largely intact — your body doesn’t break it down into glucose the way it does starches and sugars. Since net carbs count the carbohydrate left over once the listed fiber is taken out, fiber doesn’t belong in that number. Total carbs include fiber; net carbs don’t. That’s the entire distinction.

This is also why a food can look carb-heavy on the “Total Carbohydrate” line and show a much lower net figure — a cup of raspberries has about 15g total carbs, but 8g of that is fiber, leaving 7g net.

How many net carbs are in common foods?

Figures below are typical USDA FoodData Central values for these foods in common preparations — exact numbers vary by brand, ripeness, and cooking method.

Food (typical serving)	Total carbs	Fiber	Net carbs
Avocado, ½ medium	6g	5g	1g
Broccoli, 1 cup cooked	11g	5g	6g
Raspberries, 1 cup	15g	8g	7g
Spinach, 1 cup raw	1g	1g	0g
Almonds, 1 oz (23 nuts)	6g	3.5g	2.5g
Cauliflower, 1 cup	5g	2g	3g
Chia seeds, 1 oz	12g	10g	2g
Whole milk, 1 cup	12g	0g	12g
White bread, 1 slice	13g	0.5g	12.5g
Black beans, ½ cup cooked	20g	7.5g	12.5g

A pattern shows up fast: vegetables and high-fiber foods keep their net carb count low even when the total looks higher than expected. Refined grains and dairy carry most of their carbs as sugar or starch, so total and net carbs land close together.

Where do people get net carbs wrong?

Three mistakes come up constantly:

Trusting a package’s “net carbs” claim without checking the math. Brands calculate net carbs in different ways — some subtract sugar alcohols in full, others only partly, and rounding varies. Doing the subtraction yourself from the Total Carbohydrate, Fiber and Sugar Alcohol lines shows what a front-of-package number is built from.

Forgetting that “net carbs” isn’t an FDA-regulated term. Total carbs and fiber are legally defined on nutrition labels. “Net carbs” is an industry convention, not a standardized one — which is exactly why the formula matters more than any single product’s claim.

Subtracting fiber without checking whether sugar alcohols are already baked into the total. A product’s “Total Carbohydrate” line already includes any sugar alcohols it contains — that’s how the label math works. Subtracting only fiber from a product that also has 8g of erythritol leaves that erythritol in the count; the fuller formula above takes sugar alcohols out as well.

Tracking to a tight net-carb ceiling

Some people work with a much lower daily ceiling than typical keto guidance — 15 to 20g net carbs a day, a range sometimes discussed alongside modified Atkins-style protocols. At that range the margin for error all but disappears: a single food’s fiber or sugar-alcohol figure being off by even a few grams can eat a meaningful share of the whole day’s budget. That’s exactly where getting the fiber breakdown right — not just the total — matters most: the formula above is the same regardless of the ceiling, but the room for rounding error at 15g is nowhere near what it is at 100g.

What’s the simplest way to stay accurate?

The formula itself is simple. The tedious part is doing the subtraction correctly, food after food, meal after meal — and trusting that the total-carb and fiber numbers you’re subtracting are actually right in the first place. That’s the part TwentyGrams handles: every food is matched against USDA data where it exists and against other sources where it doesn’t, and net carbs are computed from the total-carb and fiber values on record, with the sugar-alcohol rule above applied where a sugar-alcohol figure is recorded.

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