Insulin Dosage Calculator

About the Insulin Dosage Calculator

Insulin dosing is one of the most complex aspects of diabetes management, requiring calculation of multiple components: total daily dose (TDD), basal-to-bolus split, insulin sensitivity factor (ISF), insulin-to-carb ratio (ICR), and correction doses. Errors in any component can lead to dangerous hypoglycemia or inadequate glucose control, making a transparent worksheet useful for review conversations and scenario checks.

This insulin dosage calculator estimates TDD using weight-based formulas or accepts known TDD values, divides the daily dose into basal (long-acting) and bolus (mealtime) components using the standard 50/50 split, calculates ISF using the 1800 rule (for rapid-acting insulin), derives the ICR using the 500 rule, and computes both carb-based meal boluses and correction doses in real-time. It covers common educational scenarios with adjustable starting factors.

For Type 1 diabetes, typical TDD ranges from 0.4 to 0.8 units/kg/day, with 0.5–0.6 being average for adults not in the honeymoon phase. For Type 2 diabetes, initial TDD is often 0.5–0.7 units/kg/day but may escalate to 1.0–2.0 units/kg/day due to insulin resistance. The calculator provides estimated and customizable factors so the arithmetic behind each component remains visible.

When This Page Helps

Insulin arithmetic involves multiple interdependent calculations — TDD, basal/bolus split, ISF, ICR, carb counting, and correction — that are easy to mix up. This calculator performs those computations together and keeps the assumptions visible so the numbers can be checked consistently.

How to Use the Inputs

1. Enter body weight in kg or lb and select diabetes type.
2. Choose whether to estimate TDD from weight or enter your known TDD.
3. Enter the carbohydrate content of the current meal in grams for bolus calculation.
4. Enter the current blood glucose level and select units (mg/dL or mmol/L).
5. Set the target blood glucose (common targets: 100–130 mg/dL pre-meal).
6. Optionally override the auto-calculated ISF and ICR.
7. Review basal dose, meal bolus, correction dose, and total mealtime reference dose.

Example Calculation

Tips & Best Practices

• Use the same units throughout the calculation.
• Keep any custom factor visible so the result can be reviewed later.
• The 1800 and 500 rules are estimate formulas, not fixed constants.
• Record the inputs used for the worksheet if you need to compare scenarios later.
• Compare the output against a separate calculation if the result matters operationally.

Reading the Worksheet

This page keeps the arithmetic for TDD, basal/bolus split, ISF, ICR, and correction dose in one place. It is useful for comparing scenarios where the underlying assumptions differ.

Reference Tables

The tables show how the rules behave over a range of TDD values. That makes it easier to see how the outputs move when the inputs change.

Units and Assumptions

The worksheet assumes consistent units and a single reference factor set. If you change the inputs, the outputs will change accordingly.

Frequently Asked Questions

• What is the 1800 rule for insulin?

  The 1800 rule estimates the insulin sensitivity factor (ISF) for rapid-acting insulin. Divide 1800 by the total daily dose (TDD): ISF = 1800 ÷ TDD. The result tells you how many mg/dL your blood glucose will drop per 1 unit of rapid-acting insulin. For regular insulin, the 1500 rule is used instead.

• What is the 500 rule for carb ratio?

  The 500 rule estimates the insulin-to-carb ratio (ICR): divide 500 by TDD. The result tells you how many grams of carbohydrates are covered by 1 unit of rapid-acting insulin. For example, TDD of 50 units → ICR = 1:10, meaning 1 unit covers 10 grams of carbs.

• How is the basal/bolus split determined?

  The standard starting split is 50% basal / 50% bolus. Some patients may need a 40/60 or 60/40 split based on their meal patterns and glucose profiles. The bolus portion is typically divided equally among three meals unless meal sizes vary significantly.

• What is a correction dose?

  A correction dose (also called a corrective or supplemental dose) is additional rapid-acting insulin given to lower an elevated blood glucose back to target. It's calculated as: (current BG - target BG) ÷ ISF. It's added to the meal bolus at mealtime or given alone between meals.

• How is the total daily dose estimated?

  The worksheet uses either a weight-based factor or a user-entered TDD. That choice then drives the rest of the arithmetic.

• Why does the result change over time?

  The calculation changes when weight, the reference factor, glucose target, or carb input changes. The page only reflects the values entered into it.