Insulin Dose Calculator

Insulin Dosing: A Weight-Based Approach

Insulin dosing for basal-bolus therapy begins with estimating the total daily dose (TDD) based on body weight. The standard starting dose for most adults is 0.5 units/kg/day, as recommended by the American Diabetes Association (ADA) Standards of Care. This initial estimate accounts for the average insulin requirement of both type 1 and type 2 diabetes patients, though individual needs vary considerably based on insulin sensitivity, body composition, residual beta-cell function, diet, and physical activity.

Understanding Total Daily Dose (TDD)

The TDD represents all insulin a patient requires over 24 hours, including both basal (background) and bolus (mealtime) insulin. For type 1 diabetes, TDD typically ranges from 0.4 to 1.0 units/kg/day. For type 2 diabetes, TDD can range from 0.3 to 2.0+ units/kg/day depending on the degree of insulin resistance. Key factors that influence TDD include:

• Body weight and BMI: Higher BMI generally correlates with greater insulin resistance and higher TDD requirements.
• Renal function: Declining kidney function reduces insulin clearance, requiring lower doses (25–50% reduction for eGFR <50).
• Age: Elderly patients are more susceptible to hypoglycemia and often require conservative dosing (0.3 units/kg/day).
• Corticosteroid use: Glucocorticoids significantly increase insulin resistance, often requiring 0.7–1.0+ units/kg/day.
• Pregnancy: Insulin requirements change throughout pregnancy, typically increasing in the second and third trimesters.

Basal-Bolus Split: The 50/50 Paradigm

In physiologic insulin replacement, approximately 50% of the TDD is given as basal insulin to suppress hepatic glucose production between meals and overnight, while the remaining 50% is divided among meals as bolus insulin to cover carbohydrate intake and correct hyperglycemia. This 50/50 split is a starting point — some patients do better with 40/60 (less basal, more bolus) if they consume carb-heavy meals, or 60/40 (more basal, less bolus) if fasting hyperglycemia is the primary issue.

Correction Factor: The 1800 and 1500 Rules

The correction factor (also called insulin sensitivity factor or ISF) estimates how much 1 unit of insulin will lower blood glucose. For rapid-acting insulin (lispro, aspart, glulisine), the formula is 1800 ÷ TDD. For regular insulin, the formula is 1500 ÷ TDD. The difference reflects the faster onset and shorter duration of rapid-acting analogs. For example, a patient with TDD of 60 units using rapid-acting insulin has a correction factor of 1800 ÷ 60 = 30 mg/dL per unit. This means each unit of insulin is expected to lower blood glucose by approximately 30 mg/dL.

Insulin-to-Carbohydrate Ratio: The 500 Rule

The carbohydrate ratio estimates how many grams of carbohydrate are covered by 1 unit of rapid-acting insulin, calculated as 500 ÷ TDD. A patient with TDD of 50 units has a carb ratio of 500 ÷ 50 = 10, meaning 1 unit of insulin covers 10 grams of carbohydrate. This ratio helps patients calculate mealtime bolus doses based on carbohydrate counting. The 500 rule provides a starting estimate; actual ratios may vary by meal and time of day, and should be refined through postprandial glucose monitoring.

Special Populations

Renal impairment: The kidney is responsible for approximately 30–80% of insulin clearance. As eGFR declines, insulin half-life increases, raising the risk of hypoglycemia. Guidelines recommend reducing TDD by ~25% for eGFR 10–50 mL/min and by ~50% for eGFR <10 mL/min or patients on dialysis.

Elderly patients: The Endocrine Society and ADA recommend less stringent glycemic targets (A1c <8.0% or <8.5%) and conservative insulin dosing (0.3 units/kg/day) in older adults to minimize hypoglycemia risk, which is associated with falls, cognitive decline, and cardiovascular events.

Hospitalized patients: Basal-bolus insulin is preferred over sliding scale alone for non-critically ill hospitalized patients with hyperglycemia. Target glucose is typically 140–180 mg/dL. Umpierrez et al. demonstrated superior glycemic control with basal-bolus regimens compared to sliding scale insulin in general surgery and medical patients.

Key References

• American Diabetes Association. Standards of Care in Diabetes — 2024. Diabetes Care. 2024;47(Suppl 1):S158–S178.
• Endocrine Society. Management of Hyperglycemia in Hospitalized Patients in Non-Critical Care Setting. J Clin Endocrinol Metab. 2022;107(8):2101–2128.
• Umpierrez GE, et al. Randomized study of basal-bolus insulin therapy in the inpatient management of patients with type 2 diabetes (RABBIT 2 trial). Diabetes Care. 2007;30(9):2181–2186.
• Davidson PC, et al. Analysis of guidelines for basal-bolus insulin dosing: basal insulin, correction factor, and carbohydrate-to-insulin ratio. Endocr Pract. 2008;14(9):1095–1101.
• Corsino L, Dhatariya K, Umpierrez GE. Management of diabetes and hyperglycemia in hospitalized patients. In: Feingold KR, et al., eds. Endotext. MDText.com; 2017.