Insulin Dosage Calculator

Insulin Dosage Calculator for Endocrinology. The output is a conservative starting point, not a final prescription. Beginning at 0.3–0.4 units/kg/day rather than 0.5 reduces early hypoglycemia in older or leaner patients, and many clinicians start type 2 patients on basal-only (0.1–0.2 units/kg) before adding prandial insulin. Titrate basal by 2–4 units (or ~10–15%) every 2–3 days to a fasting glucose target (commonly 80–130 mg/dL), and adjust carb ratios and correction factors based on postprandial patterns. Rising or persistently low readings mean the coefficients, not just the dose, need revision.

How this calculator works

This tool estimates a starting total daily dose (TDD) of insulin from body weight using weight-based coefficients, typically 0.3–0.5 units/kg/day for insulin-naive adults (lower end for the elderly, renal impairment, or type 1 at onset; higher for obesity or marked hyperglycemia). It then partitions the TDD, most commonly 50% as basal (long-acting) and 50% as prandial rapid-acting insulin split across three meals. For prandial coverage it also derives an insulin-to-carbohydrate ratio using the 500 rule (500 / TDD = grams of carbohydrate covered by 1 unit) and a correction/sensitivity factor using the 1800 rule for rapid-acting analogs (1800 / TDD = mg/dL drop per unit; the 1500 rule is the older regular-insulin variant).

When to use this calculator

Use it to initiate or transition a patient to a basal-bolus (multiple daily injection) regimen and to set carbohydrate-counting and correction parameters at the bedside or in clinic. It applies to insulin-naive adults with type 1 or type 2 diabetes and to inpatients being switched off sliding-scale-only orders. Do not use the raw weight-based output unadjusted in advanced chronic kidney disease or on dialysis, in acute illness or DKA/HHS (which require IV insulin protocols), in pregnancy, or in children without pediatric-specific dosing, where clearance and requirements differ substantially.

Inputs used

  • Weight
  • Current glucose
  • Target glucose
  • Insulin sensitivity factor
  • Carbohydrate ratio
  • Meal carbohydrates

Clinical interpretation

The output is a conservative starting point, not a final prescription. Beginning at 0.3–0.4 units/kg/day rather than 0.5 reduces early hypoglycemia in older or leaner patients, and many clinicians start type 2 patients on basal-only (0.1–0.2 units/kg) before adding prandial insulin. Titrate basal by 2–4 units (or ~10–15%) every 2–3 days to a fasting glucose target (commonly 80–130 mg/dL), and adjust carb ratios and correction factors based on postprandial patterns. Rising or persistently low readings mean the coefficients, not just the dose, need revision.

Worked example

An 80 kg insulin-naive adult with type 2 diabetes at 0.5 units/kg/day gives a TDD of 40 units. Split 50/50 yields 20 units basal glargine at night and roughly 6–7 units rapid-acting before each of three meals. The 500 rule gives an insulin-to-carb ratio of 500/40 = 1 unit per ~12.5 g carbohydrate; the 1800 rule gives a correction factor of 1800/40 = 45 mg/dL drop per unit, so a pre-meal glucose of 250 mg/dL against a 150 mg/dL target needs about (250−150)/45 ≈ 2 correction units added to that meal's dose.

Limitations and safety notes

Weight-based TDD systematically overestimates requirements in the elderly, in type 1 diabetes near diagnosis (honeymoon phase), and in renal impairment where insulin clearance falls, raising hypoglycemia risk; it can underdose the severely insulin-resistant obese patient. The 500 and 1800 rules assume rapid-acting analogs and stable, predictable eating—they mislead with regular insulin (use 450 and 1500), grazing, gastroparesis, high alcohol intake, or glucocorticoid use. The tool cannot account for illness, activity, or steroid-driven swings and does not replace continuous glucose monitoring-guided titration.

Frequently asked questions

Why is 50/50 the default basal-to-bolus split?

A 50% basal, 50% prandial division approximates normal physiologic insulin secretion for most adults on a mixed diet. Patients with large or carbohydrate-heavy meals may need a bolus-heavier split, while those who skip meals or eat lightly often do better with a slightly larger basal fraction.

Should I use 0.3 or 0.5 units/kg/day to start?

Use the lower end (0.3–0.4) for older adults, lean patients, type 1 at onset, or reduced kidney function to limit hypoglycemia. Reserve 0.5 units/kg or higher for obese, markedly insulin-resistant, or severely hyperglycemic patients, and always titrate to fasting and postprandial targets.

What is the difference between the 1800 and 1500 rules?

Both estimate the correction factor (glucose drop per unit). The 1800 rule applies to rapid-acting analogs like lispro, aspart, or glulisine; the older 1500 rule was derived for regular insulin, which is less potent per unit in this context. Match the rule to the insulin you prescribe.

Can I use this output for a sick or hospitalized patient?

Only cautiously. This estimates a subcutaneous basal-bolus starting regimen, which is superior to sliding-scale-only insulin for stable inpatients. It is not appropriate for DKA, HHS, or critical illness, which require intravenous insulin infusions, nor should the full outpatient dose be applied unadjusted when oral intake is unreliable.

References

  • Umpierrez GE, Smiley D, Zisman A, 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. PMID: 17513708.
  • American Diabetes Association Professional Practice Committee. 9. Pharmacologic Approaches to Glycemic Treatment: Standards of Care in Diabetes-2024. Diabetes Care. 2024. PMID: 38078590.
  • Umpierrez GE, Smiley D, Hermayer K, et al. Randomized study comparing a basal-bolus with a basal plus correction insulin regimen for the hospital management of medical and surgical patients with type 2 diabetes: Basal Plus trial. Diabetes Care. 2013. PMID: 23435159.

Editorial review and citation methodology

Reviewed by the Quick Medical Calculator Editorial Team. Last reviewed: May 28, 2026. The review checks calculator inputs, intended population, interpretation, limitations, and source alignment.

  • Prefer original validation studies for scoring systems and prediction tools.
  • Use current specialty society guidance, transplant allocation policy, public health guidance, or regulator resources when they govern clinical use.
  • Include limitations and safety notes when a calculator is population-specific, context-dependent, or unsuitable as a standalone decision tool.

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