Insulin Dosage Calculator

Think of insulin dosing like adjusting the temperature in a room with two separate controls: one for where the room is now versus where you want it, and one for the heat you are about to add. The correction dose handles the gap between your current blood glucose and your target. The mealtime dose handles the carbohydrates you are about to eat, which will raise your blood glucose over the next few hours.

The correction dose divides the gap between current and target blood glucose by your insulin sensitivity factor. If your blood glucose is 180 mg/dL and your target is 100 mg/dL, and each unit of insulin drops you by 40 mg/dL, you need 2 units to close that gap. The mealtime dose divides your planned carbohydrate intake by your insulin-to-carb ratio. If you are eating 60 grams of carbs and one unit covers 15 grams, that is 4 units for the meal.

The total dose adds both components together. This is the standard bolus calculator formula used in clinical insulin pumps and structured self-management programs. The math is simple, but the inputs — particularly ISF and ICR — must come from your care team because they are calibrated to your body, your insulin type, and often your time of day.

Use this calculator when you need a quick reference for a bolus dose before a meal or to correct a high blood glucose reading. It works best when you already know your ISF and ICR from a recent care team visit, your blood glucose reading is fresh and accurate, and you have not taken insulin in the last 3-4 hours.

This calculator is appropriate for adults with type 1 or type 2 diabetes who use rapid-acting insulin and have established dose parameters. It mirrors the logic in standard clinical bolus calculators.

Do not use this calculator when you are ill, under significant physical or emotional stress, or if your ISF and ICR have not been reviewed recently — all of these conditions alter your actual insulin response. Do not use it as a substitute for an insulin pump with IOB tracking if you use one. And do not use it for basal insulin calculations — this tool only covers rapid-acting (bolus) insulin.

The most common mistake is using a daytime ISF for a nighttime correction. ISF is not constant — most people are more insulin-resistant in the morning and more sensitive at night. Using the wrong ISF at the wrong time is how overcorrections happen. The consequence is nocturnal hypoglycemia, which can be dangerous and is often silent.

The second mistake is estimating carbohydrates loosely and treating the result as precise. A 20-gram error in a 60-gram meal is a 33% miss on the mealtime dose. Restaurant portions, mixed dishes, and sauces are notoriously hard to estimate. The mealtime dose this calculator returns is only as accurate as the carb count you enter — it does not compensate for guessing.

The third mistake, specific to this calculator, is ignoring insulin on board. If you took a correction dose 90 minutes ago and blood glucose has not responded yet, a second full correction will likely cause a crash. This tool has no IOB input by design — it is a reference calculation, not a pump controller. Before acting on the result, mentally account for any insulin still active from your last dose.

Correction dose = (Current BG - Target BG) / ISF

Mealtime dose = Carbohydrate grams / Insulin-to-Carb Ratio

Total dose = Correction dose + Mealtime dose

If the correction dose is negative (meaning BG is already below target), it reduces the mealtime dose rather than adding to it. The displayed total is clamped at zero — you would not take a negative dose.

This formula assumes all variables are constant, which is a simplification. ISF varies with stress, illness, activity level, and time of day. ICR can differ between breakfast and dinner for many people. Insulin-on-board (active insulin from a previous dose) is not included here — if you dosed within the last 3-4 hours, your active insulin could significantly reduce the dose you need now. Insulin pump users typically have IOB subtracted automatically; pen users must account for it manually.

The formula treats ISF as a linear constant, but physiologically, insulin sensitivity follows a curve — a high-glucose state is often accompanied by insulin resistance, meaning the effective ISF at 350 mg/dL may be meaningfully lower than the ISF at 180 mg/dL. Some clinical pump algorithms use glucose-dependent ISF adjustments. This tool does not model that curve, so large corrections at very high BG readings may underestimate the dose required to reach target.