Enter your Total Daily Dose (TDD) of insulin to estimate a carb-to-insulin ratio (ICR) using the "500 Rule" (or "450 Rule"). This is only a starting-point estimate of how many grams of carbohydrate one unit of insulin covers - not your actual prescribed ratio.
⚠️ Medical Disclaimer - Please Read
This tool is for educational and reference purposes only and cannot replace medical diagnosis or treatment decisions. This calculator gives only a rough starting-point estimate - your actual individual carb-to-insulin ratio can vary significantly based on blood sugar response, activity level, and other medications.
⚠️ Dose Change Warning
Do not change your insulin dose or carb-to-insulin ratio based on this calculator's result alone. Adjusting insulin doses carries serious risks such as hypoglycemia and hyperglycemia - always consult your doctor or diabetes care team before making any adjustment.
Carb-to-Insulin Ratio
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Grams of carbohydrate per 1 unit of insulin
⚠️ Dose Change Warning
Do not change your insulin dose or carb-to-insulin ratio based on this calculator's result alone. Adjusting insulin doses carries serious risks such as hypoglycemia and hyperglycemia - always consult your doctor or diabetes care team before making any adjustment.
The ICR indicates how many grams of carbohydrate one unit of insulin can cover while keeping blood sugar in a normal range after a meal. It is used by people with type 1 diabetes or those on intensive insulin therapy for type 2 diabetes to calculate mealtime insulin doses.
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The 500 Rule and 450 Rule
500 Rule: ICR(g) = 500 ÷ TDD The most widely used starting-point formula for rapid-acting insulin or multiple daily injection (MDI) therapy.
450 Rule: ICR(g) = 450 ÷ TDD Sometimes used as an alternative for regular (non-rapid-acting) insulin or in cases of insulin resistance.
Example: TDD of 50 units 500 Rule: 500 ÷ 50 = 10g per unit
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Why Is This Only a "Starting Point"?
The 500/450 rules are population-average estimates that do not reflect individual response. The actual ICR must be fine-tuned gradually with a medical team while monitoring post-meal blood sugar, and it is often set differently for morning, afternoon, and evening.
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How to Use the ICR
Mealtime insulin dose = grams of carbohydrate to be eaten ÷ ICR (grams per unit). For example, with an ICR of 10 and a 60g-carb meal, the estimated mealtime insulin is about 6 units. This calculation does not include a separate correction dose for high blood sugar.
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Signs the ICR May Need Adjustment
Discuss re-adjusting your ICR with your medical team if: • Post-meal (2-hour) blood sugar is consistently high or low • Hypoglycemia occurs repeatedly • Body weight, activity level, or pregnancy status changes significantly • You start or stop other medications
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Awareness of Hypoglycemia Risk
Applying the wrong ICR can result in hypoglycemia (dizziness, cold sweats, altered consciousness, etc.) or hyperglycemia. If hypoglycemia symptoms appear, consume fast-acting carbohydrates immediately and seek emergency help if needed.
Frequently asked questions
Can I apply the result from this calculator directly?
No. This calculator only gives a starting-point estimate based on the 500/450 rules. Your actual ICR must be determined and adjusted through your doctor's or diabetes care team's prescription and ongoing blood sugar monitoring.
Should I use the 500 Rule or the 450 Rule?
The 500 Rule is commonly used for rapid-acting insulin or multiple daily injections, while the 450 Rule is sometimes considered as an alternative for regular (non-rapid-acting) insulin or insulin resistance. Always consult your medical team about which is appropriate for you.
How do I find my Total Daily Dose (TDD) of insulin?
TDD is the sum of all insulin used in a day (basal + mealtime + correction doses). You can find this from your insulin pump or dosing records, and it is best calculated together with your medical team for accuracy.