Net Carbs CalculatorTotal Carbs − Fiber − Sugar Alcohols, Done Right
Turn any nutrition label into accurate net carbs. Each sweetener (erythritol, allulose, maltitol, xylitol) is weighted correctly, US and UK/EU labels are handled differently, and you can see how much of your daily keto limit one food uses.
Built & medically reviewed by Manzoor Ahmad, Pharmacist & Calculator Developer · Updated
Sugar-alcohol factors follow published glycemic data (Livesey 2003) and FDA and EU labelling rules.
How do you calculate net carbs?
Net carbs = total carbohydrate − fibre − sugar alcohols on a US label. Subtract erythritol and allulose fully, and only half of maltitol, xylitol and sorbitol, because they partly raise blood sugar. On UK, EU and Australian labels, fibre is already excluded from carbohydrate, so don’t subtract it again. Example: 24 g total − 9 g fibre − 8 g erythritol = 7 g net carbs.
Read your label
US labels include fibre in “Total Carbohydrate”.
How much of your daily limit?
7 g = 35% of your 20 g daily limit.
Which sugar alcohols count toward net carbs?
Sugar alcohols are absorbed to very different degrees. These are the factors we use, with each sweetener’s glycemic index (GI).
| Sweetener | Glycemic index | Calories / g | Counted in net carbs |
|---|---|---|---|
| Erythritol | 0 | 0.2 | 0% (fully subtract) |
| Allulose | ≈ 0 | 0.4 | 0% (fully subtract) |
| Xylitol | 7–13 | 2.4 | 50% |
| Sorbitol | ≈ 9 | 2.6 | 50% |
| Isomalt | ≈ 9 | 2.0 | 50% |
| Maltitol | ≈ 35 | 2.1 | 50% (some count 100%) |
| Stevia / monk fruit | 0 | 0 | Not a carb, so ignore |
| Sucralose (pure) | 0 | 0 | Not a carb, but packets contain dextrose |
The net carb formula
The biggest mistake I see is subtracting fibre from a UK or EU label, where it has already been excluded. That makes the food look lower in carbs than it is.
Keto protein bar (US label)
- Total carbohydrate: 24 g
- Dietary fibre: 9 g
- Erythritol: 8 g (fully subtracted)
- Net = 24 − 9 − 8 = 7 g net carbs
- That’s 35% of a 20 g keto limit. If the bar used maltitol instead of erythritol, it would be 24 − 9 − 4 = 11 g.
Sugar alcohols: tummy trouble and a pet-safety warning
Sorbitol and maltitol are poorly absorbed and pull water into the gut. More than 20–30 g at once often causes gas, bloating or diarrhoea. Sorbitol is even used in some liquid laxatives. If you have IBS, polyols are a classic FODMAP trigger. Xylitol is extremely toxic to dogs, even in small amounts, so keep xylitol gum and sugar-free sweets away from pets.
If you dose insulin for carbs, check your glucose after new “low net carb” products. Your real response may not match the label.
Related calculators
Net Carbs calculator FAQs
On US labels: net carbs = total carbohydrate − dietary fibre − sugar alcohols. Erythritol and allulose are fully subtracted, while maltitol, xylitol and sorbitol are usually counted at half. On UK/EU labels, fibre is already excluded, so only subtract sugar alcohols.
For keto and low-carb diets, net carbs are what matter for ketosis, because fibre and erythritol don’t raise blood sugar. For diabetes insulin dosing, many diabetes teams prefer total carbs, or individual testing, because sugar alcohol effects vary.
No. Fully subtract erythritol and allulose. Count xylitol, sorbitol, isomalt and maltitol at about half, because they’re partly absorbed and raise blood sugar. Maltitol has the biggest effect, with a GI of about 35.
In effect, yes. UK, EU and Australian labels list ‘carbohydrate’ without fibre, so it’s already close to net carbs. Only subtract sugar alcohols (polyols), never fibre.
No. The FDA doesn’t regulate or define ‘net carbs’, so brands calculate it differently. That’s why it’s worth recalculating from the label’s actual numbers.
Most keto diets keep net carbs at 20–50 g a day. Starting at 20 g makes ketosis most reliable.
Manzoor Ahmad
Pharmacist · Supplement & Nutrition Writer (9+ yrs) · Calculator Developer (13+ yrs)
I’m a practising pharmacist and I build DexoCalc’s calculators. I’ve spent years reading supplement and ‘keto’ food labels. The two most common net-carb errors I see are counting maltitol as zero and subtracting fibre twice from EU labels, and this calculator fixes both.
References
- Livesey G. Health potential of polyols as sugar replacers. Nutr Res Rev. 2003;16(2):163–191. PubMed
- FDA. How to Understand and Use the Nutrition Facts Label.
- EU Regulation (EU) No 1169/2011 on food information to consumers, Annex XIV (polyol and fibre energy values).
- FDA. Paws Off Xylitol; It’s Dangerous for Dogs.
- Atkinson FS, et al. International tables of glycemic index and glycemic load values: 2021. Am J Clin Nutr. 2021;114(5):1625–1632. PubMed
Disclaimer: Net carbs are estimates, and individual blood-sugar responses vary. People with diabetes should confirm their responses with glucose monitoring and follow their care team’s carb-counting method.