Insulin-to-Carb Ratio

What Is an Insulin-to-Carbohydrate (I:C) Ratio?

The insulin-to-carb ratio tells you how many grams of carbohydrates are covered by one unit of rapid-acting insulin. It’s a key factor in calculating mealtime insulin doses, especially for people with type 1 or type 2 diabetes on intensive insulin therapy.

Why It Matters

Using an accurate I:C ratio helps maintain stable blood glucose levels after meals. Without proper coverage, blood sugar can spike or drop depending on the mismatch between carbs consumed and insulin administered.

Common Calculation Methods

Method	Description
500 Rule	Divide 500 by your total daily insulin dose (TDD). Result is your I:C ratio.
Weight-Based	Uses your body weight and TDD for a more personalized estimate.

Example Using 500 Rule

• Total Daily Insulin = 40 units
• 500 ÷ 40 = 12.5
• 1 unit of insulin covers 12.5g of carbs

Time-Based Adjustments

Your body’s insulin sensitivity may vary throughout the day. Many people require different ratios in the morning versus the evening. Here’s a typical pattern:

• Morning: Lower ratio (e.g. 1:10) — more insulin needed
• Afternoon: Standard ratio (e.g. 1:12-15)
• Evening: Higher ratio (e.g. 1:15-18) — less insulin needed

Important Considerations

• This calculator provides an estimate. Real-world I:C ratios are best determined through monitoring and feedback.
• Your doctor or diabetes educator may suggest ratios tailored to your age, weight, activity level, or type of insulin.
• Always verify results before adjusting insulin doses on your own.

How to Use the Insulin-to-Carb Ratio Calculator

This calculator estimates your insulin-to-carbohydrate (I:C) ratio — the number of grams of carbohydrates that one unit of insulin will cover. It supports two methods: the 500 Rule and a weight-based formula.

Step-by-Step Instructions

1. Select a Calculation Method:
   • 500 Rule: Divides 500 by your total daily insulin dose
   • Weight-Based: Uses your weight and insulin total to calculate a ratio
2. Enter Your Total Daily Insulin:
   This includes all basal and bolus insulin taken over 24 hours.

Example (500 Rule)

• Total Daily Insulin = 40 units
• 500 ÷ 40 = 12.5
• Your I:C ratio is 1 unit of insulin for every 12.5g of carbohydrates

Time-of-Day Adjustments

Insulin sensitivity may vary throughout the day. This calculator adjusts ratios accordingly:

• Morning: Lower ratio (e.g. 1:10) — more insulin may be needed
• Afternoon: Standard ratio (e.g. 1:12.5)
• Evening: Higher ratio (e.g. 1:14) — less insulin may be needed

Note

This calculator provides a general estimate. Your actual ratio may differ based on your body, meals, and insulin type. Always consult your healthcare provider before making dosing decisions.