Printed on 2/13/2026
For informational purposes only. This is not medical advice.
The insulin correction factor (also called insulin sensitivity factor) estimates how much one unit of insulin will lower blood glucose, measured in mg/dL per unit. The 1800 rule is used for rapid-acting insulin (lispro, aspart, glulisine) and the 1500 rule for regular insulin. These are starting estimates that should be adjusted based on individual patient response.
Formula: 1800 Rule: CF = 1800 ÷ TDD; 1500 Rule: CF = 1500 ÷ TDD
Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.
The correction factor (CF) tells you how many mg/dL one unit of insulin will lower your blood glucose. For example, if your CF is 45, then 1 unit of insulin will lower your blood glucose by approximately 45 mg/dL. It is used to calculate correction doses for hyperglycemia.
The 1800 rule (CF = 1800 ÷ TDD) is used for rapid-acting insulin analogs (lispro, aspart, glulisine). The 1500 rule (CF = 1500 ÷ TDD) is used for regular insulin. The different numbers account for the different pharmacokinetic profiles.
Example: Target glucose 120 mg/dL, current glucose 240 mg/dL, CF = 45. Correction dose = (240 − 120) ÷ 45 = 2.7 units, rounded to 3 units. Add this to any meal-time insulin dose. Always account for insulin-on-board from recent doses.
If correction doses consistently fail to bring glucose to target, the CF may be too high (not enough insulin per unit). If glucose drops too low after correction, the CF may be too low. Adjust in 10–20% increments and monitor for 3–5 days before adjusting again.