Insulin Sensitivity Factor Calculator (1800 Rule)
Estimate correction factor from total daily insulin dose.
Enter your values
ⓘ Live results
Results
- Insulin sensitivity factor
- 45 mg/dL per unit
- In mmol/L per unit
- 2.5
Quick answer
The 1800 rule estimates that one unit of rapid-acting insulin lowers blood glucose by 1800 divided by the total daily insulin dose, in mg/dL.
ISF (mg/dL) = 1800 / TDD
How to use the Insulin Sensitivity Factor Calculator (1800 Rule)
- 1Enter your total daily insulin dose (basal + bolus) in units.
- 2The 1800 rule is a common starting estimate for rapid-acting insulin correction factors.
- 3This is an educational estimate only — insulin dosing must be individualised and supervised by your diabetes care team.
Worked example
Using the values the calculator loads with:
Inputs
- Total daily insulin dose40 units
Results
- Insulin sensitivity factor45 mg/dL per unit
- In mmol/L per unit2.5
Frequently asked questions
Is 1800 always right?
No — some clinicians use the 1500 rule for regular insulin; individual sensitivity varies and should be verified by testing.
What is ISF used for?
It helps calculate a correction dose to bring high blood glucose back to target.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.