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.