What is Insulin Sensitivity Factor (ISF)?

ISF, also called the correction factor, is the number of mg/dL that one unit of insulin is expected to lower blood glucose. For example, an ISF of 50 means one unit drops blood sugar by approximately 50 mg/dL.

What is the 1800 Rule vs the 1700 Rule?

The 1800 Rule (ISF = 1800 ÷ TDI) applies to regular insulin, which acts more slowly. The 1700 Rule (ISF = 1700 ÷ TDI) applies to rapid-acting analogs like lispro, aspart, and glulisine, which peak faster and require a slightly lower divisor.

What counts as Total Daily Insulin (TDI)?

TDI is the total number of insulin units you take in a typical day, including all basal (long-acting or pump basal) and all bolus (mealtime + correction) doses. Use a 3–7 day average for accuracy.

Is this calculator a substitute for medical advice?

No. The 1800/1700 rule provides an estimated starting point. Your actual ISF may differ based on insulin resistance, activity, illness, and other factors. Always work with your endocrinologist or diabetes care team to verify any insulin adjustments.

What if I use an insulin pump?

Pump users typically use the 1700 Rule with rapid-acting insulin. TDI should include total basal delivery (basal rate × 24 h) plus all boluses. Many pump systems calculate ISF automatically, but this tool lets you cross-check manually.

Insulin Sensitivity Factor Calculator

Name: Insulin Sensitivity Factor Calculator
Availability: InStock
Author: Nham Vu

Calculate your Insulin Sensitivity Factor (ISF) to find out how many mg/dL one unit of insulin lowers your blood glucose.

Enter Your Insulin Data

Total Daily Insulin (TDI) — units/day

Sum of all basal + bolus units per day (3–7 day average recommended).

Insulin Type

Rapid-acting

Humalog, NovoLog, Apidra

Regular

Humulin R, Novolin R

Target Blood Glucose — mg/dL (optional)

Used to calculate a sample correction dose if your current BG is above target.

Current Blood Glucose — mg/dL (optional)

Typical ISF Ranges

Insulin-sensitive (e.g. child, lean type 1) 50–100 mg/dL/unit

Typical adult type 1 30–50 mg/dL/unit

Adult with insulin resistance 15–30 mg/dL/unit

High resistance / large TDI < 15 mg/dL/unit

These are rough benchmarks. Individual ISF depends on activity, stress, illness, and other factors.

Medical disclaimer: This tool provides an educational estimate only. Do not adjust insulin doses without guidance from a licensed healthcare provider.

Summary

Calculate your Insulin Sensitivity Factor (ISF) to find out how many mg/dL one unit of insulin lowers your blood glucose.

How it works

Enter your Total Daily Insulin (TDI) — the sum of all basal and bolus insulin units you take per day.
Select your insulin type: rapid-acting (e.g. Humalog, NovoLog, Apidra) or regular (e.g. Humulin R).
The calculator applies the appropriate rule: 1700 ÷ TDI for rapid-acting, or 1800 ÷ TDI for regular insulin.
Your ISF is displayed in mg/dL per unit — meaning one unit of insulin lowers blood glucose by that amount.
Use the result as a starting point; always confirm your ISF with your healthcare provider.

Use cases

Estimating a correction dose when blood glucose is above target.
Verifying whether your current correction factor aligns with the 1800/1700 rule.
Adjusting insulin therapy when total daily dose changes.
Teaching patients or students how ISF is derived from TDI.
Comparing ISF across different insulin types.
Supporting diabetes educators and endocrinologists in clinical discussions.

Frequently Asked Questions

Last updated: 2026-07-23 · Reviewed by Nham Vu