Starting Point Estimator

Understanding the Mathematics of Insulin Settings

IMPORTANT: This tool is an educational model designed to visualize the mathematical formulas often used to derive theoretical starting points for insulin pump or MDI settings. It is not a medical calculator and does not provide dosing recommendations.

In diabetes education, settings are often illustrated using weight-based calculation chains. This model allows users to observe how those calculations function by entering a single physical metric (weight) and selecting a theoretical physiological profile (insulin sensitivity). The model then estimates the three pillars of insulin management:

• Basal Rate: Background metabolic insulin.

• Insulin-to-Carb Ratio (ICR): The theoretical grams of carbohydrate covered by one unit.

• Insulin Sensitivity Factor (ISF): The theoretical blood glucose drop expected from one unit.

The model functions on a "waterfall" logic, where the result of the first step provides the data for every subsequent calculation.

1. The Foundation: Weight (Kg)

Standard dosing formulas are commonly calculated in kilograms. The model first converts the input (lbs) into kilograms (kg) to standardize the data.

2. The Engine: Total Daily Dose (TDD)

This is the critical variable. The model calculates a Theoretical Total Daily Dose using the formula: Weight (kg) × Factor = TDD.

The Factor: This variable adjusts the equation based on observed physiological benchmarks often cited in clinical literature:

• 0.45 (Sensitive): Often associated with high activity levels or the "honeymoon" phase.

• 0.55 (Standard): A common textbook benchmark for many adults.

• 0.65+ (Resistant): Often associated with puberty, illness, or higher insulin resistance.

3. The Split: Basal (50%)

Standard insulin therapy theory assumes that a human body utilizes approximately 50% of its insulin for background metabolic function (Basal) and 50% for food (Bolus).

• The model calculates TDD × 0.50 to find a theoretical daily basal need.

• It divides that result by 24 hours to display a specific hourly pump rate.

4. The Inverse: ICR & ISF

Once the model establishes a TDD, it applies standard "Rules of Insulin" to estimate bolus ratios.

• For Carbs (Rule of 500): The model divides 500 by the TDD. Mathematically, a higher TDD results in a stronger ratio (lower number).

• For Corrections (Rule of 1800): The model divides 1800 by the TDD. A higher TDD results in a stronger correction factor (lower number).

Limitations of Mathematical Models

Why These Numbers Are Estimates (Not Prescriptions)

While these formulas are standard in textbooks, human biology is highly variable. This tool provides a "Starting Line," not a "Finish Line." Here is why these theoretical numbers may not align with real-world needs:

1. The "Ghost Low" Phenomenon The math assumes a perfect 50/50 split. However, if a real-world Basal rate is set too weak, blood sugar may sit higher than intended. When a bolus is given for food, that insulin effectively does "double duty"—covering the meal and filling the deficit left by the weak basal. This creates the visual illusion of needing a stronger carb ratio, when the actual physiological need is more basal. A calculator cannot detect this dynamic; only basal testing can reveal it.

2. Variable Resistance The model assumes insulin resistance is flat across 24 hours. In reality, many people experience "Foot on the Floor" (morning resistance) or higher sensitivity in the afternoon. This tool estimates a flat basal rate (e.g., 1.0u/hr), whereas real-world needs often vary hour-to-hour.

3. The Law of Large Numbers The rules (Rule of 500, Rule of 1800) are based on population averages. They generally apply to the middle 80% of the population. Outliers—those who are extremely sensitive or extremely resistant—may find these standard rules too aggressive or too conservative.

4. Lifestyle Factors The model processes weight, but it does not account for lifestyle variables. It cannot adjust for low-carb diets (which alter insulin needs), athletic training, or medications (such as steroids) that impact resistance.

5. Absorption Issues The math assumes that 1 unit of insulin acts as 1 unit of insulin. It does not account for scar tissue (lipohypertrophy), site failures, or bad infusion sets, which can cause a full dose to behave like a partial dose.

Summary

Use this tool to understand the math behind the settings. Use your own data (CGM and BGM) to refine your management. If the calculated values suggest a Basal of 1.0, but your fasting data shows hypoglycemia, the calculation does not match your physiology. Always listen to your body over the calculator.

Disclaimer: This content is for educational purposes only and is not medical advice. It is not intended to replace the clinical judgment of a healthcare professional. Always consult your physician before making changes to your insulin therapy.