Your insulin correction factor (also called insulin sensitivity factor) represents how many mg/dL one unit of insulin is expected to lower your blood glucose. The 1800 rule result applies to rapid-acting insulin analogs (lispro, aspart, glulisine), while the 1500 rule result applies to regular insulin. For example, a correction factor of 50 means one unit of rapid-acting insulin should lower blood glucose by approximately 50 mg/dL.

To calculate a correction dose, subtract your target glucose from your current glucose and divide by the correction factor. If the result is a fraction, rounding to the nearest half or whole unit is typical. Always account for insulin on board — insulin from recent doses that is still active — to avoid dose stacking, which can cause dangerous hypoglycemia. These are starting estimates; your actual sensitivity may differ based on activity level, illness, stress, and time of day.

Use this calculator when establishing an initial insulin correction factor for a patient starting or adjusting a basal-bolus insulin regimen. It is most commonly used for patients with type 1 diabetes or insulin-dependent type 2 diabetes who need correction doses for hyperglycemia above their target glucose range.

It is also useful when reviewing and recalibrating an existing correction factor — for instance, when a patient's total daily insulin dose changes significantly due to weight gain, lifestyle changes, or medication adjustments. Endocrinologists and diabetes educators frequently use this as a teaching tool to help patients understand how their correction doses are derived.

The 1800 and 1500 rules are population-level estimates and do not account for individual variability in insulin sensitivity. Factors such as insulin resistance, renal function, hepatic function, concurrent medications (steroids, for example), stress, illness, and physical activity can all significantly alter a patient's actual response to insulin.

These rules assume a relatively stable total daily dose and steady-state insulin requirements. In patients with highly variable glucose patterns, gastroparesis, or rapidly changing clinical status (such as during hospitalization), the correction factor may need frequent adjustment. The calculator does not account for insulin on board from recent boluses, which is critical to avoid dose stacking.

Pediatric patients, pregnant patients, and patients with extreme insulin sensitivity or resistance may require different approaches. Always verify correction factor estimates against actual patient glucose response data over several days before relying on them.