How to Calculate Insulin Dose — ICR & ISF Guide

Informational Guide · 2026

The Bolus Calculation Formula

Calculating an insulin bolus dose involves two separate components:

• Meal dose = Carbohydrates (g) ÷ ICR
• Correction dose = (Current glucose − Target glucose) ÷ ISF
• Total dose = Meal dose + Correction dose

This is the standard bolus formula used by endocrinologists worldwide for people with Type 1 diabetes and insulin-dependent Type 2 diabetes. Our free bolus insulin calculator automates this math so you can focus on your health.

What is ICR — Insulin-to-Carb Ratio

The ICR (Insulin-to-Carb Ratio), also called the insulin to carb ratio or carb factor, tells you how many grams of carbohydrates are covered by one unit of insulin. For example, an ICR of 12 means 1 unit of insulin covers 12 grams of carbs.

Your ICR is set individually by your endocrinologist and may vary by time of day. Typical ICR values range from 6 to 25 grams per unit. Our ICR calculator uses your personal ratio to compute the meal portion of your bolus dose.

What is ISF — Insulin Sensitivity Factor

The ISF (Insulin Sensitivity Factor), also known as the correction factor, shows how much your blood glucose drops per one unit of insulin. An ISF of 2.5 mmol/L means one unit lowers your glucose by 2.5 mmol/L (about 45 mg/dL). The correction factor calculator uses ISF to determine how much correction insulin is needed.

Target Blood Glucose Level

For most adults with T1D, the recommended target is 5.0–7.0 mmol/L (90–126 mg/dL). The calculator supports both mmol/L (Europe, Canada) and mg/dL (USA) — switch with the toggle at the top of the screen.

How to Use This Insulin Dose Calculator

1. Enter your current blood glucose — measured before the meal.
2. Enter carbohydrates — total grams in your meal.
3. Enter your target glucose — set by your doctor.
4. Enter your ICR — insulin-to-carb ratio.
5. Enter your ISF — correction factor.
6. Tap Calculate dose — result is rounded to 0.5 units.

Blood Glucose Reference Ranges

• Below 3.9 mmol/L (70 mg/dL) — Hypoglycemia. Do not administer insulin.
• 3.9–7.8 mmol/L (70–140 mg/dL) — Normal range
• 7.8–11.0 mmol/L (140–198 mg/dL) — Elevated
• Above 11.0 mmol/L (198 mg/dL) — Hyperglycemia

Why This Calculator Is Different

Most insulin calculators require an account or internet connection. This free type 1 diabetes calculator is:

• Offline-first — works without internet after first visit
• No registration — open and calculate immediately
• No ads on the calculator page
• 7 languages — EN, RU, DE, FR, ES, BE, ZH
• Free forever — supported by voluntary donations

⚠️ Important: This calculator performs mathematical computation only. It does not account for active insulin on board (IOB), glycemic index, physical activity, illness, or stress. All dosing decisions must be made with your healthcare provider. This is not a certified medical device.