Insulin Sensitivity Factor Calculator (1800 Rule)
Estimate correction factor from total daily insulin dose.
Enter your values
Enter the total daily insulin dose in units.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- 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
At a glance
| What it does | Estimate correction factor from total daily insulin dose. |
|---|---|
| Category | Health |
| Inputs needed | Total daily insulin dose |
| Main output | Insulin sensitivity factor |
| Formula | ISF (mg/dL) = 1800 / TDD |
| Cost | Free — no sign-up, no download |
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.
Inputs explained
- Total daily insulin dose(units)
- Enter the total daily insulin dose in units.
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.
What do I need to enter into the Insulin Sensitivity Factor Calculator (1800 Rule)?
Just 1 value: total daily insulin dose. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Insulin Sensitivity Factor Calculator (1800 Rule) work out the 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. It applies the formula ISF (mg/dL) = 1800 / TDD and shows the working so you can check each step by hand.
Is the Insulin Sensitivity Factor Calculator (1800 Rule) free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.