💉 Insulin Dosage Estimator

Insulin dosing starts from the total daily dose (TDD): everything else is derived from it. A common starting estimate for type 1 diabetes is 0.5 to 0.6 units per kilogram per day, split roughly half basal (long-acting, background) and half bolus (rapid-acting, meals and corrections). This calculator produces that starting estimate, then derives the two workhorse ratios.

The carb ratio comes from the 500 rule: divide 500 by the TDD to get grams of carbohydrate covered by one unit. The correction factor comes from the 1800 rule: divide 1800 by the TDD to get how many mg/dL one unit lowers glucose. These are starting estimates that your endocrinologist refines with your glucose data, never final prescriptions.

How to Use This Calculator

Enter weight in kilograms. If you already take insulin and know your total daily dose, enter it for sharper ratios; otherwise leave it blank and the calculator estimates from weight. Read the TDD, the basal/bolus split, the carb ratio, and the correction factor. Bring all four numbers to your endocrinologist or diabetes educator before using any of them.

The 500 Rule and the 1800 Rule

The 0.5 to 0.6 units/kg starting range reflects measured insulin requirements in new type 1 diabetes, adjusted down for honeymoon phase or up for puberty, illness, or steroids. The 50/50 split mirrors physiology: about half of daily insulin covers background needs, half covers meals. The 500 rule is empirical: in practice, 500 divided by TDD approximates the grams of carbohydrate one unit covers. The 1800 rule similarly approximates the glucose drop per unit for rapid-acting analogs (some clinicians use 1500 for regular insulin). Both rules assume the TDD is correct, which is why a wrong TDD poisons both ratios, and why clinicians titrate from glucose logs rather than trusting the first numbers.

Worked Example

An 80 kg adult new to insulin: estimated TDD is 44 units/day, split into 22 units/day (~50%) basal and 22 units/day (~50%) mealtime. The 500 rule gives 1 unit per 11 g carbs, and the 1800 rule gives 1 unit per 41 mg/dL over target. If this person later stabilizes on a true TDD of 36 units, entering 36 refines the ratios to 1:14 and 1:50 instead. These are the textbook starting points your endocrinologist individualizes from.

Using the Ratios Safely

The carb ratio doses meals: grams of carbohydrate divided by the ratio gives mealtime units. The correction factor fixes highs: points above target divided by the factor gives correction units, usually added to the meal dose. The two biggest errors are stacking corrections too close together (rapid insulin works 3 to 5 hours, so wait before re-correcting) and treating the ratios as permanent: illness, exercise, alcohol, and menstrual cycles all shift sensitivity. Log glucose, doses, food, and activity, and review patterns with your team every few weeks.

Insulin Errors Can Kill: Get Supervision

Too much insulin causes hypoglycemia, which can injure the brain and kill; too little allows diabetic ketoacidosis. Never start, stop, or overhaul insulin on calculator output. Work with an endocrinologist and a diabetes educator, learn hypoglycemia treatment (15 grams fast carbs, recheck in 15 minutes, glucagon on hand), and wear medical ID. This tool is for informational purposes only, not medical advice. Dosing decisions must be confirmed with your doctor or pharmacist. Consult a healthcare professional.

Related tools: BMI calculator and estimated average glucose (A1C).

For informational purposes only, not medical advice. Dosing decisions must be confirmed with your doctor or pharmacist. Consult a healthcare professional.