This is how many mg/dL your blood sugar drops per 1 unit of rapid-acting insulin.
Enter as 'X:Y' (e.g., 10:1) or a single number (e.g., 15, which implies 15:1).
Understanding Carbohydrate Counting for Diabetes Management
For individuals managing diabetes, especially Type 1 diabetes or Type 2 diabetes requiring insulin, understanding and accurately counting carbohydrates is a cornerstone of effective blood glucose control. Carbohydrate counting allows for precise insulin dosing, helping to prevent hyperglycemia (high blood sugar) and hypoglycemia (low blood sugar). This calculator helps estimate the mealtime insulin dose needed based on the carbohydrates consumed and your individual insulin needs.
The Math Behind the Calculation
This calculator uses a common formula for calculating bolus insulin for meals, which is often adjusted based on your current blood glucose level and target blood glucose level.
The calculation involves two primary components:
Correction Dose (for high blood sugar): This part of the insulin dose corrects elevated blood glucose levels back to your target.
The formula is: Correction Dose = (Current Blood Glucose - Target Blood Glucose) / Insulin Sensitivity Factor (ISF)
Meal Dose (for carbohydrates): This part of the insulin dose covers the carbohydrates in the meal.
First, we need to determine the carbohydrate-to-insulin ratio. If you enter "10:1", it means 1 unit of insulin covers 10 grams of carbohydrates. If you enter "15", it implies a ratio of 15:1.
The formula is: Meal Dose = Total Carbohydrates in Meal / Carbohydrate Ratio Value (where the ratio value is the grams of carb per unit of insulin)
The total insulin dose is the sum of the correction dose and the meal dose:
Total Insulin Dose = Correction Dose + Meal Dose
Key Terms Explained:
Carbohydrates in Meal (grams): The total amount of carbohydrates you plan to eat in a single meal or snack. Carbohydrates are found in foods like bread, pasta, rice, fruits, dairy products, and sweets.
Insulin Sensitivity Factor (ISF): Also known as the Insulin-to-Carb Ratio (ICR) or Correction Factor. This number represents how sensitive your body is to insulin. A lower ISF means you need more insulin to lower your blood sugar by the same amount, and vice-versa. It's often expressed as "mg/dL per unit" or "mmol/L per unit."
Target Blood Glucose (mg/dL): The ideal blood glucose level you aim for before a meal or as a general target. This is usually set by your healthcare provider.
Current Blood Glucose (mg/dL): Your blood glucose reading taken just before you plan to eat or administer insulin.
Carbohydrate-to-Insulin Ratio: This ratio tells you how many grams of carbohydrates 1 unit of insulin can cover. For example, a 10:1 ratio means 1 unit of insulin is needed for every 10 grams of carbohydrates. This ratio can vary throughout the day (e.g., breakfast vs. dinner) and may change over time.
How to Use This Calculator:
1. Enter Carbohydrates: Input the total grams of carbohydrates in your upcoming meal or snack.
2. Enter Insulin Sensitivity Factor (ISF): Provide your ISF in mg/dL per unit. If you're unsure, consult your healthcare provider.
3. Enter Target Blood Glucose: Input your pre-meal or target blood glucose level in mg/dL.
4. Enter Current Blood Glucose: Input your most recent blood glucose reading in mg/dL.
5. Enter Carbohydrate-to-Insulin Ratio: Input your ratio. You can enter it as "X:Y" (e.g., "10:1") or as a single number representing grams per unit (e.g., "15" for a 15:1 ratio).
6. Calculate: Click the "Calculate Insulin Dose" button.
The calculator will then provide an estimated insulin dose required.
Important Disclaimer:
This calculator is a tool for estimation and educational purposes only. It is NOT a substitute for professional medical advice. Your individual insulin needs can be affected by many factors, including activity level, stress, illness, fat and protein content of meals, and the type of insulin used. Always consult with your endocrinologist, certified diabetes educator, or healthcare provider to determine the correct insulin doses and carbohydrate counting strategies for your specific situation. Do not make changes to your diabetes management plan without consulting your healthcare team.
function calculateInsulin() {
var mealCarbsInput = document.getElementById("mealCarbs");
var insulinSensitivityInput = document.getElementById("insulinSensitivity");
var targetBGInput = document.getElementById("targetBG");
var currentBGInput = document.getElementById("currentBG");
var carbRatioInput = document.getElementById("carbRatio");
var resultDiv = document.getElementById("result");
var mealCarbs = parseFloat(mealCarbsInput.value);
var insulinSensitivity = parseFloat(insulinSensitivityInput.value);
var targetBG = parseFloat(targetBGInput.value);
var currentBG = parseFloat(currentBGInput.value);
var carbRatioStr = carbRatioInput.value;
// — Input Validation —
var errors = [];
if (isNaN(mealCarbs) || mealCarbs < 0) errors.push("Carbohydrates in Meal must be a non-negative number.");
if (isNaN(insulinSensitivity) || insulinSensitivity <= 0) errors.push("Insulin Sensitivity Factor must be a positive number.");
if (isNaN(targetBG) || targetBG <= 0) errors.push("Target Blood Glucose must be a positive number.");
if (isNaN(currentBG) || currentBG 0) {
resultDiv.innerHTML = errors.join("");
resultDiv.style.backgroundColor = "#dc3545"; // Red for errors
resultDiv.style.display = "block";
return;
}
// — Parse Carb Ratio —
var carbRatioValue = 0;
if (carbRatioStr.includes(':')) {
var parts = carbRatioStr.split(':');
if (parts.length === 2) {
var carbGrams = parseFloat(parts[0]);
var insulinUnits = parseFloat(parts[1]);
if (!isNaN(carbGrams) && carbGrams > 0 && !isNaN(insulinUnits) && insulinUnits > 0) {
carbRatioValue = carbGrams / insulinUnits;
} else {
errors.push("Invalid format for Carbohydrate-to-Insulin Ratio. Use 'X:Y' with positive numbers.");
}
} else {
errors.push("Invalid format for Carbohydrate-to-Insulin Ratio. Use 'X:Y' or a single number.");
}
} else {
var singleRatio = parseFloat(carbRatioStr);
if (!isNaN(singleRatio) && singleRatio > 0) {
carbRatioValue = singleRatio; // Assumes X:1 ratio
} else {
errors.push("Invalid format for Carbohydrate-to-Insulin Ratio. Use 'X:Y' or a single number.");
}
}
if (errors.length > 0) {
resultDiv.innerHTML = errors.join("");
resultDiv.style.backgroundColor = "#dc3545"; // Red for errors
resultDiv.style.display = "block";
return;
}
// — Calculations —
var correctionDose = 0;
if (currentBG > targetBG) {
correctionDose = (currentBG – targetBG) / insulinSensitivity;
}
var mealDose = mealCarbs / carbRatioValue;
var totalInsulinDose = correctionDose + mealDose;
// Ensure the dose is not negative and round to a reasonable precision (e.g., 0.5 or 1 unit)
totalInsulinDose = Math.max(0, totalInsulinDose);
// Round to nearest 0.5 units if preferred, or just to 1 decimal place
totalInsulinDose = Math.round(totalInsulinDose * 2) / 2; // Rounds to nearest 0.5
// — Display Result —
resultDiv.innerHTML = totalInsulinDose.toFixed(1) + " units of insulin" +
"(Correction: " + correctionDose.toFixed(1) + " units | Meal: " + mealDose.toFixed(1) + " units)";
resultDiv.style.backgroundColor = "var(–success-green)"; // Green for success
resultDiv.style.display = "block";
}