This calculator estimates a starting total daily insulin dose from body weight and insulin sensitivity, then splits it into basal (long-acting) and bolus (mealtime) insulin and divides the bolus across meals. It is a clinician-facing reference and teaching tool — a starting point that must be titrated against blood-glucose readings, not a self-dosing tool for patients.

How the total daily dose is estimated

The total daily dose (TDD) is weight-based: TDD = body weight in kilograms × a units-per-kilogram factor. A widely taught starting factor is about 0.5 units/kg/day (the UCSF Diabetes Teaching Center uses 0.55), with a usable range of roughly 0.4 to 1.0 units/kg/day. The factor reflects insulin sensitivity: lean, newly-diagnosed type 1, or otherwise sensitive patients start near 0.4; a standard start is 0.5; and insulin-resistant or type 2 patients often need 0.6 to 1.0 or more.

Because the formula is defined per kilogram, weight entered in pounds is converted to kilograms first (pounds ÷ 2.2046). The result is only a starting estimate — actual requirements vary widely and are refined by titration.

Splitting basal and bolus, and dividing across meals

Once the TDD is set, it is divided into basal and bolus insulin. The conventional starting split is 50% basal and 50% bolus, though anywhere from about 40% to 60% basal is used depending on whether fasting or post-meal glucose is the bigger problem — a basal-heavy split up to ~60% is common when fasting hyperglycemia dominates. The basal portion is given as one long-acting injection; the bolus portion is split across meals, most often three, so each meal receives roughly one-sixth of the TDD.

The calculator also derives two personalized starting rules from the TDD. The Rule of 500 gives the insulin-to-carbohydrate ratio (500 ÷ TDD grams of carb per unit) and the Rule of 1800 gives the correction factor (1800 ÷ TDD mg/dL drop per unit) for rapid-acting insulin. Some references substitute 1500 for regular (short-acting) insulin.

Why every number here must be titrated

Weight-based dosing intentionally errs toward a safe, modest starting point. Real insulin needs depend on diabetes type, degree of insulin resistance, diet, physical activity, illness, stress, other medications (steroids raise needs sharply), and kidney function. Doses are adjusted over days to weeks against fasting and post-meal glucose readings — commonly changing basal by 10 to 20% every 2 to 3 days and adjusting bolus by the post-meal response — until glucose targets are met.

Insulin has a narrow safety margin, and errors can cause dangerous hypoglycemia. This tool is for clinician reference and diabetes education only; it does not replace a prescriber's individualized plan, and no one should start, stop, or change insulin based on it.