Clinical & Hospital Pharmacy
Insulin Dose & Sensitivity Calculator
Works out the insulin sensitivity factor, insulin-to-carb ratio and a pre-meal rapid-acting bolus from the total daily insulin dose.
Total rapid-acting bolus
8.8units
6.0 U meal + 2.8 U correction
Total daily dose (TDD)
All insulin in 24 hours — basal plus every meal bolus.
Sum of 24-hr basal + meal boluses. Or estimate it from weight below.
Estimate TDD from body weight
Calculates ~38.5 Units for 70 kg
Rules & glucose units
ISF rule (sensitivity)
Rapid-ActingISF = 1800 / TDD (mg/dL per unit). A higher rule number means more sensitive.
ICR rule (carb ratio)
Rapid-ActingICR = 500 / TDD (grams of carbohydrate covered by 1 unit).
Glucose units
Switching converts the glucose values below (1 mmol/L = 18.0182 mg/dL).
Before the meal
Glucose from a fingerstick or CGM, and the meal's total carbohydrate.
Fingerstick or CGM reading now.
Pre-meal target, often 80–130 mg/dL.
Total dietary carbohydrate in the meal.
Try an example patient
Working
Each step with the numbers plugged in.
1. Insulin sensitivity factor (ISF, correction factor)
ISF = Rule (1500–2200) ÷ TDD (mg/dL lowered per 1 unit) · mmol/L: ISF ÷ 18.0182
2. Insulin-to-carbohydrate ratio (ICR)
ICR = Rule (300–500) ÷ TDD (grams of carbohydrate covered per 1 unit)
3. Total bolus
Total bolus = [(current BG − target BG) ÷ ISF] + [meal carbs (g) ÷ ICR]
TDD — total daily dose (units/day); BG — blood glucose. The correction part is zero when glucose is at or below target, or below the hypoglycaemia threshold (70 mg/dL / 3.9 mmol/L). Basal and bolus are each taken as 50% of TDD, and the bolus half is spread over 3 meals.
Sensitivity bands (ISF in mg/dL per unit): > 50 highly sensitive, 30–50 average, 18–30 moderate resistance, < 18 severe resistance.
Guideline reference: American Diabetes Association (ADA) Standards of Medical Care in Diabetes and Endocrine Society clinical guidelines.
Common questions
The 1800 rule is used for rapid-acting analogues (lispro, aspart, glulisine) and the 1500 rule for regular human insulin. Higher numbers (2000, 2200) give a larger ISF and suit more insulin-sensitive patients; the 1700 rule sits between.
The calculator only adds insulin for glucose above target. It does not subtract from the meal dose when glucose is below target — decide that clinically. Below 70 mg/dL (3.9 mmol/L) it treats the reading as hypoglycaemia and withholds correction entirely.
This calculator does not subtract insulin on board (IOB). If a bolus was given in the last 3–4 hours, part of it is still acting, and giving a full correction on top can cause hypoglycaemia (insulin stacking).
No. Switching converts the glucose values and the ISF by 18.0182, so the correction dose stays the same (apart from small rounding in the converted values).
A common starting range is 0.4–1.0 units/kg/day: about 0.4–0.5 for insulin-sensitive or new type 1 patients, 0.55 as a standard starting point, and 0.7–1.0 with insulin resistance, obesity or puberty. Titrate from glucose records.
Prepared by the PharmaWallah student team. Verify results with your textbook or instructor. Report an error · Editorial policy