If you try low-carb eating, you will hear about "net carbs": total carbohydrate minus fibre. It sounds sensible, because fibre is a carbohydrate your small intestine does not break down into sugars. But whether you should subtract it depends on one thing most beginners are never told: which kind of label you are reading.
On a US-style label, "Total Carbohydrate" includes fibre, sugars and sugar alcohols. On a label made to EU rules, carbohydrate means carbohydrate the body can use, and fibre is listed on its own line. On those labels the fibre is already left out of the carbohydrate figure. Subtract it again and you count too little.
Check where the fibre sits. Listed on its own line, it is already out of the carbohydrate figure. Inside the total, you can subtract it if you follow net carbs.
EU rules define carbohydrate as any carbohydrate the body metabolises, and define fibre as carbohydrate polymers that are neither digested nor absorbed in the human small intestine. That is why the two are kept apart on EU labels. US labels work the other way round: fibre sits inside the total. The same bowl of oats can show two different carbohydrate numbers, with nothing wrong with either.
No. It is a convention from low-carb communities, and companies use it differently. Some subtract all fibre and all sugar alcohols from the total; others subtract only some. Because of that, a "net carbs" claim on a pack is worth treating with caution, and the nutrition table is the better place to look. The evidence on how low-carb eating compares with other approaches is mixed in places, and there is no single carb number that suits everyone.
This guide explains how labels work. It is not medical advice. If you have diabetes, take medication (especially for diabetes or blood pressure), are pregnant or breastfeeding, have or have had an eating disorder, or have any other condition, talk to your doctor or a registered dietitian before cutting back on carbohydrate. Fibre also does not always behave the same in the body: some types are fermented in the gut, so counting rules are a rough guide only.