Insulin-to-Carb Ratio Calculator
This insulin-to-carb ratio calculator estimates your carb ratio (rule of 500), sensitivity factor (1800 rule), and the mealtime plus correction bolus from your total daily insulin dose. It is educational — always follow your prescribed plan.
Calculator
LiveEducational tool, not medical advice. Verify every dose against the prescription and your institutional protocol — a licensed clinician is responsible for the final dose.
Estimates only. Do not change your insulin without your prescriber — dosing errors can cause severe hypoglycemia or hyperglycemia.
Enter values to see your result.
How to Use the Calculator
- Enter your total daily insulin dose (TDD).
- Enter the grams of carbohydrate for the meal.
- Optionally enter current and target blood glucose for a correction.
- Review your carb ratio, sensitivity factor, and total bolus.
What the Result Means
The carb ratio and sensitivity factor estimate a mealtime bolus and a correction, combined into a total bolus. These are educational estimates only — your prescribed ratios may differ, and you should not change insulin without your diabetes care team.
When to Use This Calculator
- Estimating an insulin-to-carb ratio
- Calculating a mealtime bolus from carbs
- Adding a correction to the meal bolus
Frequently Asked Questions
What is the insulin-to-carb ratio rule of 500?
The carb ratio estimates the grams of carbohydrate covered by 1 unit of insulin: ICR = 500 ÷ total daily dose. A TDD of 50 gives 1 unit per 10 g of carbs.
How do I calculate a mealtime bolus?
Meal bolus = grams of carbohydrate ÷ carb ratio. Add a correction dose of (current − target blood glucose) ÷ sensitivity factor when above target.
What is the correction factor (1800 rule)?
The correction (sensitivity) factor is 1800 ÷ total daily dose for rapid-acting insulin, estimating the mg/dL drop per unit. Some clinicians use the 1500 rule for regular insulin.
References & Guidelines
- American Diabetes Association. Standards of Care in Diabetes (current year).