Purpose of Bolus Insulin

People with type 1 diabetes often dose rapid-acting insulin before meals to control blood sugar spikes. This bolus dose has two parts: a meal dose that covers carbohydrates and a correction dose that accounts for differences between current blood glucose and a target level. Our calculator combines these elements to suggest an insulin amount in units. Because diabetes care is highly personal, work closely with your healthcare provider when adjusting doses.

Calculating the Meal Dose

The meal portion is based on how many grams of carbohydrates you plan to eat and your insulin-to-carb ratio. The formula is:

where $\mathrm{I\_m}$ is the meal insulin dose in units, $C$ is the grams of carbs, and $R$ is your carb ratio (grams per unit). For example, if your ratio is 10 g/U and you eat 60 g of carbs, the meal dose is 6 units.

The Correction Factor

If your blood glucose is above target before a meal, you may need additional insulin. The correction factor, sometimes called insulin sensitivity, estimates how many mg/dL your glucose drops per unit of insulin. The correction formula looks like:

Here, $B$ is the difference between current blood glucose and your target, while $F$ is the correction factor. Suppose your correction factor is 50 mg/dL per unit, your current BG is 200 mg/dL, and the target is 110 mg/dL. The difference is 90 mg/dL, so the correction dose is 90/50 = 1.8 units.

Combining Meal and Correction

After calculating each component, add them together for the total bolus:

Many insulin pumps round to the nearest half-unit or use custom increments. Your doctor might recommend rounding down if your glucose trend is falling or rounding up if you’re running high.

Example Calculation

Imagine you plan to eat 45 g of carbohydrates, your carb ratio is 12 g/U, your current BG is 180 mg/dL, your target is 100 mg/dL, and your correction factor is 40. The meal dose is 45/12 = 3.75 units. The correction dose is (180 − 100)/40 = 2.0 units. Together you’d take about 5.75 units.

Tracking and Adjustments

Record each dose and corresponding blood glucose to refine your ratios over time. Factors like exercise, stress, illness, and time of day can change insulin needs. Consult with a certified diabetes educator or endocrinologist before making significant changes.

Common Carb Ratios and Correction Factors

Carb Ratio	Who Might Use It
5 g/U	Very insulin resistant
10 g/U	Average adult
15 g/U	Insulin sensitive

Correction factors typically range from 25 to 75 mg/dL per unit. Your diabetes team determines these numbers based on patterns in your readings.

Important Safety Notes

This tool is informational only. Rapid-acting insulin is potent, and miscalculations can lead to dangerous hypoglycemia. Always double-check your entries, especially if you’re adjusting doses on your own. If you’re new to carb counting or have unpredictable blood sugars, seek professional guidance.

Conclusion

Bolus insulin dosing helps maintain stable glucose levels around meals. By combining carb ratios and correction factors, you can adapt to different foods and situations. Use this calculator as a learning tool in partnership with medical advice.