Almost everyone who tries keto runs into the same small puzzle within a day or two: the carb limit they have been given is in net carbs, but the food in front of them only lists total carbohydrate. Bridging that gap is a quick piece of arithmetic once you know which numbers to use, and it is the skill that lets you eat by feel rather than measuring everything forever. This is the practical version, food by food and label by label.

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What a net carb actually is

A net carb is the portion of a food’s carbohydrate that your body digests and turns into blood sugar. You reach it by starting with the total carbohydrate and removing the parts that pass through without raising your glucose, mainly fibre and most sugar alcohols. Fibre is carbohydrate your gut cannot break down, so it travels through largely untouched; that is why it gets subtracted. Whether you should count net carbs at all, or play it safer with total carbs, is a separate question with a good case on both sides, and the net carbs versus total carbs piece argues it properly. This article assumes you have settled on net and want to count them accurately.

The basic sum

The arithmetic is short. Take the total carbohydrate in a serving, subtract the fibre, and if any sugar alcohols are listed, subtract those too. What remains is your net carbs.

So a serving of food with 12 grams of total carbohydrate and 5 grams of fibre gives 7 grams net. A keto bar showing 20 grams of carbohydrate, 9 of fibre and 8 of sugar alcohol works out at 3 grams net on paper, though as you will see, packaged products are where that paper figure starts to lie.

Reading a Belgian or European label

Here is the wrinkle that catches every newcomer who shops in Belgium. On a European nutrition panel the line marked “glucides” in French or “koolhydraten” in Dutch already has the fibre taken out. Fibre sits on its own line, “fibres” or “vezels”, underneath. So the carbohydrate number on a Belgian, French or German label is effectively the net figure already, and subtracting fibre a second time would undercount your carbs and flatter your day.

In short, on a Belgian label you read the carbohydrate line and stop. You do not subtract the fibre, because the manufacturer already has. Getting this one habit right prevents a surprising amount of confusion, and there is more on decoding local packaging in the hidden carbs and reading labels guide.

Reading a British or American label

British and American labels work the other way. Their total carbohydrate line includes the fibre, so you do the subtraction yourself: total carbohydrate minus fibre, minus any sugar alcohols. A British label that reads 15 grams of carbohydrate “of which fibre 6 grams” gives you 9 grams net. American labels increasingly print a “total sugars” and sometimes a sugar-alcohol line as well, so on those you have everything you need on the panel.

If you buy a mix of imported and local products, which is normal in Brussels, the safest habit is to glance at the language and the layout before you do any maths. European panel, the number is ready to use. British or American panel, subtract the fibre first.

Sugar alcohols, and where the maths bends

Fibre is honest, but sugar alcohols are not all created equal, and this is the part of net-carb counting that goes wrong most often. Erythritol is barely absorbed and fair to subtract in full. Maltitol, which fills a lot of cheap sugar-free chocolate and sweets, raises blood sugar a good deal more than its marketing suggests, so subtracting all of it overstates how keto the product really is. A bar advertising “2g net carbs” through a pile of maltitol can affect you far more than the label claims. When in doubt, count maltitol closer to its full value and treat dramatic net-carb boasts on processed food with a raised eyebrow. The sweeteners and the erythritol question post goes through which ones behave and which do not.

Net carbs in everyday foods

After a week or two the numbers for the things you eat often become second nature. A rough feel for common foods, per typical serving:

Whole foods rarely trip you up, because their fibre is genuine and the sums are small. It is the engineered low-carb products, not the vegetables, that need the scrutiny. If you want a clearer sense of which plants sit where, the best and worst vegetables for keto guide sorts them out.

Letting an app do the counting

You do not have to keep this in your head. For a single food, the net carbs calculator takes total carbs, fibre and sugar alcohols and does the subtraction, with the maltitol catch handled. For a whole day, a tracking app such as one of the popular carb counters stores the net figures for thousands of foods and totals your day as you log. Used for the first fortnight, an app teaches you the numbers far faster than guessing does, after which most people stop logging and simply know. Two cautions: app entries are user-submitted and sometimes wrong, so sanity-check anything that looks too good, and when you scan a European barcode, remember the label has already removed the fibre, so the app should not remove it again.

Common mistakes when counting

A handful of errors account for most of the trouble. Subtracting fibre twice on a European label is the classic, and it quietly lets carbs creep up. Trusting the net-carb number on a maltitol-sweetened product is the next. Forgetting that “per serving” may be half the packet, so the real figure doubles, catches plenty of people. And counting only the obvious carbs while ignoring the sauce, the breading or the splash of milk in the coffee adds up across a day. None of these is hard to avoid once you know they exist; they are simply the places attention slips.

Putting it together

Net carbs are total carbohydrate minus fibre and minus the well-behaved sugar alcohols, and the only real subtlety is who has already done the fibre subtraction for you. On a Belgian or European label, the carbohydrate number is ready to use. On a British or American one, take the fibre off yourself. Be wary of processed products leaning hard on a tiny net-carb claim, lean on whole foods where the maths is honest, and let an app carry the load until the figures live in your head. Do that and counting stops being a chore within a couple of weeks.

This is general information about the ketogenic diet, not medical advice. Keto does not suit everyone; if you are pregnant, on medication, or managing a condition such as diabetes, speak to a doctor or dietitian first.