Insulin Correction & Sensitivity Calculator
Calculates insulin sensitivity factor, correction dose, and I:C ratio
Calculator
Why use it
Personalizes insulin dosing. Calculates how much 1 unit of insulin will lower blood glucose. Determines correction doses for hyperglycemia. Estimates carb coverage ratios.
About
Calculates the Insulin Sensitivity Factor (ISF/correction factor) using the 1800 rule (rapid-acting) or 1500 rule (regular insulin), the correction dose for hyperglycemia, and the Insulin-to-Carb (I:C) ratio using the 500 rule. These calculations are fundamental to diabetes management for both insulin pump users and MDI (multiple daily injection) patients.
When to use
- Setting up insulin pump parameters
- Initiating or adjusting MDI (basal-bolus) regimens
- Calculating correction doses for hyperglycemia
- Adjusting insulin-to-carb ratios
Formula
Pearls & pitfalls
- 1800 Rule (rapid-acting: lispro, aspart, glulisine): ISF = 1800 / TDD.
- 1500 Rule (regular insulin): ISF = 1500 / TDD.
- 500 Rule (I:C ratio): I:C = 500 / TDD (grams of carb per 1 unit).
- TDD = Total Daily Dose of all insulin (basal + bolus).
- These are STARTING estimates — always individualize based on monitoring.
- ISF typically ranges from 20-100 mg/dL per unit in adults.
- Sick patients, steroid use, and stress can significantly alter insulin sensitivity.
Next steps
ISF and I:C ratios are starting estimates — titrate based on glucose monitoring (CGM or SMBG). Correction dose = (Current BG - Target BG) / ISF. Review every 1-2 weeks during initiation. Always consider active insulin on board (IOB).
Evidence
The 1800 rule (Walsh et al., Pumping Insulin) and 500 rule are widely used in clinical practice and ADA/AACE guidelines. Evidence is largely empirical and consensus-based. Individualization through glucose monitoring is always required.