Health July 13, 2026 · 8 Min Read

Insulin Calculator – Guide & Formulas

Calculate insulin correction doses and mealtime carbohydrate coverage based on your personalized Insulin Sensitivity Factor (ISF) and Carb Ratio (ICR).

The Insulin Calculator is a clinical management helper designed for individuals requiring bolus insulin therapy (such as those with Type 1 or insulin-dependent Type 2 diabetes). It computes correct bolus requirements by factoring in current blood glucose, target glucose, personalized insulin sensitivity factors, and mealtime carbohydrate quantities.

Key Takeaway

Use the free Insulin Calculator to calculate insulin correction doses and mealtime carbohydrate coverage based on your personalized insulin sensitivity factor (isf) and carb ratio (icr). Get instant results with step-by-step explanations.

How to Use the Insulin Calculator

  1. Enter your current and target blood sugar levels.
  2. Input your personalized Insulin Sensitivity Factor (ISF) / Correction Factor.
  3. Enter the carbohydrate count of your upcoming meal and your Insulin-to-Carb Ratio (ICR).
  4. Review the calculated Correction Dose, Carbohydrate Coverage, and recommended Total Bolus Dose.

The Formula

Total Bolus = (Current Blood Sugar - Target Blood Sugar) / Insulin Sensitivity Factor + (Grams of Carbs / Insulin-to-Carbohydrate Ratio)

Variable Definitions

  • ISF: Insulin Sensitivity Factor: how much 1 unit of rapid-acting insulin lowers blood sugar
  • ICR: Insulin-to-Carbohydrate Ratio: the number of grams of carbs covered by 1 unit of insulin
  • Bolus: The rapid-acting insulin dose taken for meals or to correct high blood sugar

Calculating Bolus for a Meal

A user has a blood glucose of 180 mg/dL (target is 100 mg/dL). Their ISF is 40, their ICR is 10, and they plan to consume 50g of carbohydrates.

  1. Step 1: Compute correction dose: (180 - 100) / 40 = 2.0 units.
  2. Step 2: Compute carbohydrate dose: 50 / 10 = 5.0 units.
  3. Step 3: Sum the requirements: 2.0 + 5.0 = 7.0 units of rapid-acting insulin.

Frequently Asked Questions

What is the Rule of 1800 and Rule of 500 in insulin management?

These clinical rules estimate initial therapy ratios: The Rule of 1800 divides 1800 by your Total Daily Dose (TDD) of insulin to estimate your ISF. The Rule of 500 divides 500 by TDD to estimate your ICR. Ratios must be confirmed and monitored with your endocrinologist.

What is active insulin (insulin on board)?

Insulin on Board (IOB) represents the insulin from a previous dose that is still actively lowering blood glucose. Failing to account for active insulin when calculating a correction can lead to "stacking" and severe hypoglycemia (low blood sugar).