Question 1

What is the insulin Total Daily Dose (TDD)?

Accepted Answer

TDD is the sum of all insulin used over 24 hours — basal + pre-meal bolus + corrections. Initial literature estimates: T1D ≈ 0.5 U/kg/day, T2D ≈ 0.4 U/kg/day, gestational diabetes ≈ 0.8 U/kg/day. Actual TDD varies with insulin resistance, disease stage, physical activity, puberty and other individual factors.

Question 2

What is the 500 (and 450) rule for ICR?

Accepted Answer

The 500 Rule (rapid-acting insulin — lispro, aspart, glulisine) estimates the Insulin-to-Carb Ratio (ICR): ICR = 500 ÷ TDD. Result: 1 unit of insulin covers that number of grams of carbohydrate. For regular (human) insulin, the numerator is 450 (slower onset). Published by John Walsh in Pumping Insulin (6th ed., 2017).

Question 3

What is the 1800 (and 1500) rule for ISF?

Accepted Answer

The 1800 Rule (rapid-acting insulin) estimates the Insulin Sensitivity Factor (ISF) in mg/dL: ISF = 1800 ÷ TDD. Result: 1 unit of insulin lowers blood glucose by that mg/dL amount. For regular insulin, use 1500. In mmol/L, numerators are 100 (rapid) and 83 (regular). Also described in Walsh & Roberts.

Question 4

How is the Correction Dose calculated?

Accepted Answer

Correction Dose = (Current BG − Target BG) ÷ ISF. Example: if current glucose is 250 mg/dL, target is 120 mg/dL and ISF = 50 mg/dL per unit, the correction = (250 − 120) ÷ 50 = 2.6 U. The total pre-meal bolus adds the correction to the carbohydrate bolus (gCHO ÷ ICR).

Question 5

What is the difference between rapid and regular insulin in the calculations?

Accepted Answer

Rapid-acting analogs (lispro, aspart, glulisine) have onset of action in 5–15 min, peak 45–90 min and duration 3–5 h. Regular (human) insulin starts at 30 min, peaks 2–4 h and lasts 6–8 h. Since regular is slower and more prolonged, the same unit covers more carbohydrate (ICR = 450/TDD) and lowers glucose less sharply (ISF = 1500/TDD mg/dL).

Question 6

Does this calculator prescribe insulin?

Accepted Answer

No. It is a strictly educational tool to illustrate formulas described in the literature (Walsh & Roberts 2017; ADA Standards of Care). Decisions about insulin regimens, dose adjustments, hyperglycemia correction and titration require individualized medical evaluation, continuous monitoring and adjustments based on real patient glucose values.

Educational Insulin Calculator

1. Patient data

2. Calculate dose for a meal

3. Calculated parameters

4. Recommended dose (educational)

How do these formulas work?

500 rule (rapid) / 450 rule (regular)

1800 rule (rapid) / 1500 rule (regular)

Insulin on Board (IOB)

Essential notice