Insulin Correction Factor Calculator
Use the 1800 Rule to estimate your insulin sensitivity factor — how much one unit of rapid-acting insulin lowers your blood sugar. This is a starting estimate; your actual factor may vary.
Calculate Your Correction Factor
Enter your total daily dose to estimate your insulin sensitivity factor.
Calculate Correction Dose
Optional — enter your current and target blood sugar to estimate how many units to correct.
Enter your TDD above first to enable this section.
Common Correction Factors (Rapid-Acting Insulin)
Based on the 1800 Rule (mg/dL) and 100 Rule (mmol/L).
| TDD | 1800 Rule (mg/dL) | 100 Rule (mmol/L) |
|---|---|---|
| 20 units | 90 mg/dL | 5.0 mmol/L |
| 30 units | 60 mg/dL | 3.3 mmol/L |
| 40 units | 45 mg/dL | 2.5 mmol/L |
| 50 units | 36 mg/dL | 2.0 mmol/L |
| 60 units | 30 mg/dL | 1.7 mmol/L |
Medical Disclaimer
This calculator is for educational purposes only. Always consult your doctor or diabetes educator before adjusting insulin doses. Individual responses to insulin vary significantly.
Glucoly – Blood Sugar Tracker
Track insulin doses and blood sugar together
Log your insulin doses alongside glucose readings in Glucoly to see patterns: how your correction doses perform, what your average correction is, and whether your factor needs adjusting.
What Is the Insulin Correction Factor?
Also called the Insulin Sensitivity Factor (ISF), this number tells you how many mg/dL (or mmol/L) one unit of rapid-acting insulin will lower your blood sugar. It is used to calculate correction doses when blood sugar is above target.
The 1800 Rule vs the 1500 Rule
The 1800 Rule is used for rapid-acting insulins (Humalog, NovoLog, Fiasp, Lyumjev). The 1500 Rule is used for regular insulin (Humulin R, Novolin R). Both divide a constant by your Total Daily Dose to get your correction factor.
For mmol/L users, the equivalent constants are 100 (rapid-acting) and 83 (regular insulin).
How to Use Your Correction Factor
If your blood sugar is 220 mg/dL and your target is 100 mg/dL, and your correction factor is 40:
- Subtract target from current: 220 − 100 = 120 mg/dL above target
- Divide by correction factor: 120 ÷ 40 = 3 units
Always verify with your care team before acting on any calculated dose.
Important Limitations
The 1800 and 1500 rules are population-level estimates. Your actual correction factor may differ due to insulin resistance, illness, stress, physical activity, or time of day. These formulas are a starting point for discussion with your endocrinologist or diabetes educator, not a substitute for personalised clinical guidance.
Sources
- Walsh J, Roberts R, Bailey T. Guidelines for Optimal Bolus Calculator Settings in Adults. J Diabetes Sci Technol. 2011;5(1):129-135. PMC3045237
- American Diabetes Association. Pharmacologic Approaches to Glycemic Treatment. Diabetes Care. 2024;47(Suppl 1):S158-S178.
- Bergenstal RM. Insulin dose titration for type 2 diabetes mellitus. Mayo Clin Proc. 2007;82(1):115-119.
- Davidson PC, Hebblewhite HR, Steed RD, Bode BW. Analysis of guidelines for basal-bolus insulin dosing: basal insulin, correction factor, and carbohydrate-to-insulin ratio. Endocr Pract. 2008;14(9):1095-1101.