Build a meal, see total carbohydrate, fibre, net carbs, and protein, and (optionally) calculate the matching bolus insulin dose. Pick foods from the searchable list, set portion size, and the totals update as you go. Carbohydrate values come from USDA FoodData Central with cross-checks against the Diabetes UK food data tables.

Carb & Bolus Calculator

Food	Portion (g)	Carbs	Fibre	Net carbs	Protein
No items yet — pick a food above to start.

Optional: bolus insulin estimate

Insulin-to-carb ratio (1 unit per X g)

Current glucose (mmol/L)

Target glucose (mmol/L)

Insulin sensitivity factor (1 unit drops mmol/L by)

Bolus dose is for reference only. Always confirm with your diabetes team. Many factors (illness, exercise, hormones, fat/protein content of meal) alter the actual insulin you need. People on insulin should never change doses based solely on this tool.

How carb counting works

Carbohydrate is the macronutrient with the largest direct effect on blood glucose. For people on mealtime (“bolus”) insulin, matching insulin to grams of carbohydrate is the foundation of accurate dosing — and the basis of every modern insulin pump’s bolus calculator.

Total carbohydrate = the carbs declared on a food label or in a food table.
Fibre doesn’t raise glucose for most people, so it’s typically subtracted to give “net carbs.”
Net carbs = total − fibre. Useful, but check what your team prefers — UK practice typically dose-counts total carbs, while US and ketogenic communities use net carbs.
Protein has minimal acute glucose effect in most people but a large protein meal (~30 g+) can raise glucose 2–3 hours later, particularly in type 1 diabetes — discuss “protein insulin” rules with your team if this affects you.

How the bolus calculation works

Two numbers do most of the work:

Insulin-to-carb ratio (ICR or I:C): how many grams of carbs are covered by 1 unit of rapid-acting insulin. A typical adult ICR is 1:8 to 1:15 grams per unit, but yours is whatever your team has set for you.
Insulin sensitivity factor (ISF) / correction factor: how much 1 unit drops your glucose. Typical adult range: 1 unit drops 1.5–4 mmol/L (27–72 mg/dL).

The calculator uses:

Carb dose = total carbs ÷ ICR
Correction dose = (current glucose − target) ÷ ISF, but only if current glucose is above target
Total dose = carb dose + correction dose

This is the same logic used by every bolus advisor on every pump and CGM-linked glucometer. Your real prescriber-approved settings come from your team — never make them up from a calculator.

What this calculator does not account for

Insulin on board (insulin from a previous bolus that’s still working). Pumps track this; this tool doesn’t.
Fat & protein impact on delayed glucose rise after high-fat or high-protein meals.
Glycaemic index/load — refined carbs hit faster than slow-release ones; some people split or “extend” their bolus to match.
Exercise in the next several hours, which can drop glucose substantially.
Illness, hormonal cycles, dawn phenomenon and other variables that change ICR/ISF day-to-day.

Frequently asked questions

Should I count total carbs or net carbs?

Whichever your diabetes team taught you. UK-trained teams usually count total carbohydrate; many US patients and most ketogenic communities count net carbs (total − fibre). Both work — the key is consistency, so your insulin doses match your tracking.

Where do these carb values come from?

The food table is built from USDA FoodData Central with cross-checks against Diabetes UK food data. Cooked weights are used where applicable. Real-world values vary by brand, recipe, and cooking method by ±20% — always check the label when one is available.

What if my food isn’t on the list?

Use the closest analogue, or check the package label, or use the free USDA FoodData Central database. UK shoppers can use the carb-per-100 g value on any nutrition label — that’s the same unit this tool uses.

Why does my pump suggest a different dose?

Pump bolus calculators include “insulin on board” — the residual insulin from your last bolus that’s still working. That can reduce the suggested dose. If yours differs from this tool by more than a unit or two, trust the pump (or your team’s calculation).

Can I use this on a low-carb diet?

Yes — it works the same way. Add your foods, see total carbs, dose accordingly. People following a ketogenic or very-low-carb diet will see almost no carb bolus at most meals; the tool will still flag any correction dose if your starting glucose is above target.

Related guides

References: USDA FoodData Central. Diabetes UK food data tables. NICE NG17 (Type 1 diabetes in adults). NICE NG18 (Type 1 and 2 diabetes in children and young people). ADA Standards of Care 2026. Reviewed: May 2026.

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