How this insulin dosing calculator works
This calculator estimates a mealtime bolus insulin dose using common basal-bolus therapy concepts: carb coverage plus correction insulin, then subtracting insulin on board (IOB). It is designed for people who already have personalized settings from their diabetes care team.
It can help with carb counting decisions for rapid-acting insulin and provide a transparent breakdown of the math. You still need to use your own treatment plan, including sick-day rules, exercise adjustments, and guidance for pump or pen users.
The formula used
1) Carbohydrate dose
Carb dose = Meal carbs (g) ÷ Insulin-to-carb ratio (g per unit)
2) Correction dose
Correction dose = (Current BG − Target BG) ÷ Correction factor
If current glucose is below target, this part becomes negative and reduces the total dose.
3) Subtract active insulin
Total recommended dose = Carb dose + Correction dose − IOB
The tool then rounds to your selected increment (for example, nearest 0.5 units) and applies an optional max bolus safety cap.
Input guide (what each field means)
- Current blood glucose: Your latest meter/CGM value used for correction.
- Target blood glucose: Typical pre-meal target set by your clinician.
- Carbohydrates: Total grams you plan to eat now.
- Insulin-to-carb ratio: How many grams are covered by 1 unit of insulin.
- Correction factor (ISF): How much 1 unit lowers your glucose.
- IOB: Rapid insulin still active from prior dose.
Example calculation
Suppose your current glucose is 190 mg/dL, target is 110 mg/dL, you plan to eat 60g carbs, your insulin-to-carb ratio is 1:12, your correction factor is 50 mg/dL per unit, and your IOB is 1.0 unit.
- Carb dose: 60 ÷ 12 = 5.0 units
- Correction dose: (190 − 110) ÷ 50 = 1.6 units
- Before IOB: 5.0 + 1.6 = 6.6 units
- After IOB: 6.6 − 1.0 = 5.6 units
- Rounded to nearest 0.5: 5.5 units
Important safety reminders
- Always follow your personalized diabetes treatment plan first.
- If blood glucose is below 70 mg/dL, treat hypoglycemia before dosing insulin for food.
- If blood glucose is very high (for example, above 250–300 mg/dL), follow ketone and sick-day instructions.
- Alcohol, exercise, stress, illness, and timing of insulin can significantly change dose needs.
- Children, pregnancy, and people with kidney disease need individualized medical supervision.
When to contact your healthcare team
Reach out promptly if you have recurring lows, persistent highs, frequent ketones, or repeated uncertainty about dosing. A diabetes educator or endocrinology team can refine your insulin sensitivity factor, carb ratio, and target glucose safely.