Carbohydrate Ratio Calculator
Estimate your Insulin-to-Carb Ratio (ICR) to determine mealtime insulin doses.
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Result
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Formula
The "Rule of 500" is a standard estimate used by many clinicians to find a starting point for carbohydrate counting.
Worked Example
Understanding Your Insulin-to-Carb Ratio
- Formula: ICR = 500 / Total Daily Dose (TDD). A TDD of 50 gives a ratio of 1:10
- Typical ratios range from 1:5 (insulin resistant) to 1:20 (insulin sensitive)
- Ratios may differ by meal. Many people need more insulin at breakfast (e.g., 1:8) than at dinner (e.g., 1:12)
- The Rule of 500 is a starting estimate. Fine-tuning is done by reviewing post-meal glucose readings
- Exercise, illness, and stress can all temporarily change your effective carb ratio
This calculator provides a starting estimate. Work with your endocrinologist or diabetes educator to fine-tune your ratio using post-meal glucose data.
You can also calculate changes using our Insulin Correction Dose Calculator or HbA1c to eAG Calculator.
Frequently Asked Questions
What does a carb ratio of 1:10 mean?
It means you take 1 unit of rapid-acting insulin for every 10 grams of carbohydrates you eat. If a meal has 60g of carbs, you would take 6 units.
Why is the number 500 used?
The Rule of 500 is a clinically validated heuristic for rapid-acting insulin analogs. It estimates that one day's insulin covers about 500 grams of carbohydrate in total. For regular insulin, some clinicians use the Rule of 450.
Should I adjust my ratio if I exercise?
Yes. Exercise increases insulin sensitivity, so many people increase their carb ratio (take less insulin) before or after activity. Some reduce their mealtime dose by 25% to 50% around exercise.
Can my ratio change throughout the day?
Yes. Due to hormonal patterns like the dawn phenomenon, many people need a tighter ratio (more insulin per gram) at breakfast compared to lunch or dinner.
How do I know if my ratio is correct?
Check blood sugar 2 to 3 hours after a meal. If it rises more than 40 to 60 mg/dL above pre-meal level, your ratio may be too high (not enough insulin). If it drops below target, the ratio may be too low.
Is the Rule of 500 accurate for everyone?
It is a starting point. Children, highly active individuals, and those with significant insulin resistance may need substantial adjustments. Regular review with a diabetes care team is recommended.
Medical Disclaimer
This calculator is provided for informational and educational purposes only. It is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making any decisions based on these results. Do not disregard or delay seeking medical advice because of information obtained from this tool.
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I can help you understand the carbohydrate ratio calculator formula, interpret your results, and answer follow-up questions.
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Our AI assistant provides general estimates and advice only. Please consult a qualified healthcare professional before making any health-related decisions.
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