Insulin Bolus Calculator — Rex's Toolbox

Rex says

Same equations the textbooks use — just way less awkward. Pop in your stats and I'll tell you what the number actually means for you.

Try a scenario

Click to load — tweak from there.

Inputs

Carbohydrates in meal(g)

Insulin-to-carb ratio (1 unit per X g)

Current blood glucose(mg/dL)

Target glucose(mg/dL)

Correction factor (mg/dL per unit)

Total daily dose(units)

Result

Total bolus (units)

6.6

Meal coverage (units)

5.00

Correction dose (units)

1.56

Suggested I:C from 500 rule

11.9

Suggested correction factor (1800 rule)

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How to use this

1Enter carbohydrates in meal (g).
2Enter insulin-to-carb ratio (1 unit per x g).
3Enter current blood glucose (mg/dL).
4Enter target glucose (mg/dL).
5Enter correction factor (mg/dl per unit).
6Enter total daily dose (units).
7Read your total bolus (units) on the right — it updates as you type.
8Hit Share to keep the scenario or send it to someone.

About this calculator

Combine a carbohydrate bolus with a correction dose using your insulin-to-carb ratio and correction factor, and see the sensitivity factors the 500 and 1800 rules suggest from your total daily dose.

FormulaBolus = carbs ÷ I:C ratio + (current BG − target) ÷ correction factor.

Worked example

Using the values the calculator loads with:

Inputs

Carbohydrates in meal: 60 g
Insulin-to-carb ratio (1 unit per X g): 12
Current blood glucose: 180 mg/dL
Target glucose: 110 mg/dL
Correction factor (mg/dL per unit): 45
Total daily dose: 42 units

Results

Total bolus (units): 6.6
Meal coverage (units): 5
Correction dose (units): 1.56
Suggested I:C from 500 rule: 11.9
Suggested correction factor (1800 rule): 43

What each field means

Inputs

Carbohydrates in meal (g): The carbohydrates in meal used in the calculation, measured in g. Starts at 60 g so you have a working example on load.
Insulin-to-carb ratio (1 unit per X g): The insulin-to-carb ratio (1 unit per x g) used in the calculation. Starts at 12 so you have a working example on load.
Current blood glucose (mg/dL): The current blood glucose used in the calculation, measured in mg/dL. Starts at 180 mg/dL so you have a working example on load.
Target glucose (mg/dL): The target glucose used in the calculation, measured in mg/dL. Starts at 110 mg/dL so you have a working example on load.
Correction factor (mg/dL per unit): The correction factor (mg/dl per unit) used in the calculation. Starts at 45 so you have a working example on load.
Total daily dose (units): The total daily dose used in the calculation, measured in units. Starts at 42 units so you have a working example on load.

Results

Total bolus (units): Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Meal coverage (units): Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Correction dose (units): Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Suggested I:C from 500 rule: Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Suggested correction factor (1800 rule): Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.

FAQ

Should I use this to dose insulin?

No. Use it to understand the arithmetic and sanity-check a plan your care team set. Insulin dosing decisions belong with your clinician.

Why do the 500/1800 rules differ from my settings?

They're starting estimates. Real ratios vary by time of day, activity, and insulin type, and get tuned from logged data.

Accuracy and limitations

Population formulas describe averages; individual bodies vary, especially at the extremes of height, age, or muscle mass.
Results do not account for medical conditions, medication, or pregnancy.
Use this as a directional reference, not a diagnosis — talk to a clinician before acting on it.

Cite this calculator

Writing about this topic? Grab a citation — every link helps keep these tools free.

APA

RevenueLab. (2026). Insulin Dose & Carb Ratio Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/insulin-carb-ratio

HTML

<p>Source: <a href="https://www.revenuelab.fyi/toolbox/insulin-carb-ratio" target="_blank" rel="noopener">Insulin Dose & Carb Ratio Calculator — RevenueLab</a> (2026).</p>

Markdown

Source: [Insulin Dose & Carb Ratio Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/insulin-carb-ratio) (2026).