Insulin Calculator Formulas Reference

By Ryan Mitchell · Reviewed against ADA Standards of Care · Updated July 2026

Every equation used across this site, in one place, with its meaning and the tool that runs it. Bookmark this as your cheat sheet — full sourcing is on the methodology page.

Dosing formulas

Total Daily Dose (TDD)

TDD = Weight (kg) × 0.4–0.6 u/kg/day

Starting estimate of all insulin per day. Insulin-naïve Type 2: 0.1–0.2 u/kg or 10 u fixed. ➜ Dose by Weight · TDD

Basal / Bolus Split

Basal = TDD × 40–50% · Bolus pool = TDD × 50–60%

➜ Basal-Bolus · Basal %

Insulin-to-Carb Ratio (ICR)

ICR = 500 ÷ TDD (rapid) · 450 ÷ TDD (Regular)

Grams of carb covered by 1 unit. ➜ ICR (500) · 450 Rule · Compare 450/500/550

Insulin Sensitivity Factor (ISF)

ISF = 1800 ÷ TDD (rapid) · 1500 ÷ TDD (Regular)

mg/dL that 1 unit lowers glucose. ➜ ISF Calculator

Correction & Meal Dose

Correction = (Current BG − Target) ÷ ISF · Meal = Carbs ÷ ICR

Total bolus = meal + correction − insulin on board. ➜ Correction · Bolus · IOB

Insulin resistance & metabolic

HOMA-IR

(Fasting glucose × Fasting insulin) ÷ 405 [mg/dL] · ÷ 22.5 [mmol/L]

➜ HOMA-IR · guide: What Is HOMA-IR?

QUICKI

1 ÷ [log(fasting insulin) + log(fasting glucose)]

➜ QUICKI

Monitoring & conversion

GMI (Glucose Management Indicator)

GMI (%) = 3.31 + 0.02392 × mean glucose (mg/dL)

➜ GMI Calculator

eAG ↔ HbA1c

eAG (mg/dL) = 28.7 × A1c − 46.7

➜ HbA1c Calculator

Glucose units

mg/dL = mmol/L × 18.018 · mmol/L = mg/dL ÷ 18.018

➜ Glucose Converter

Insulin units ↔ mL

mL = units ÷ concentration (U-100 = 100, U-40 = 40, U-500 = 500)

➜ Units ↔ mL · Units ↔ mg

Sources

Full citations for every formula above are consolidated on our methodology page — ADA Standards of Care, Walsh & Roberts (500/1800 Rules), Matthews 1985 (HOMA-IR), Katz 2000 (QUICKI), Bergenstal 2018 (GMI), Nathan 2008 (eAG).

Last reviewed: July 2026