Insulin Dose Calculator
Calculate insulin dose based on carb intake, correction factor, and current blood glucose. Enter values for instant results with step-by-step formulas.
Reviewed for accuracy by Rahul Singh, Health & Wellness Specialist
Medical disclaimer: This calculator is provided for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment. Results are general estimates and may not reflect your individual circumstances. Always consult a qualified healthcare professional before making decisions about your health.
Insulin Dose Calculator
Calculator
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Formula: Total Dose = (Carbs / ICR) + ((Current BG - Target BG) / CF) - IOB
Worked example — Total Dose: 6.5 units | Carb Coverage: 4.5u | Correction: 1.8u
Formula
Total Dose = (Carbs / ICR) + ((Current BG - Target BG) / CF) - IOB
The insulin dose has three components: carb coverage (grams of carbohydrates divided by the insulin-to-carb ratio), correction dose (the glucose amount above target divided by the correction factor), and insulin on board subtraction (previously administered insulin still active). The final dose is the sum of carb and correction doses minus IOB, with a floor of zero to prevent negative dosing.
Worked Examples
Example 1: Standard Meal Bolus with Correction
Problem:Current glucose is 210 mg/dL, target is 120 mg/dL, eating 45g carbs, ICR is 1:10, correction factor is 50, no insulin on board.
Solution:Carb dose = 45g / 10 = 4.5 units Correction dose = (210 - 120) / 50 = 90 / 50 = 1.8 units Total dose = 4.5 + 1.8 = 6.3 units No IOB adjustment needed Rounded dose = 6.5 units (nearest 0.5)
Result:Total Dose: 6.5 units | Carb Coverage: 4.5u | Correction: 1.8u
Example 2: Dose with Insulin On Board
Problem:Glucose is 250 mg/dL, target 120, eating 30g carbs, ICR 1:12, correction factor 40, 2 units of IOB remaining.
Solution:Carb dose = 30g / 12 = 2.5 units Correction dose = (250 - 120) / 40 = 130 / 40 = 3.25 units Subtotal = 2.5 + 3.25 = 5.75 units Minus IOB = 5.75 - 2.0 = 3.75 units Rounded dose = 4.0 units
Result:Total Dose: 4.0 units | Before IOB: 5.75u | IOB Deducted: 2.0u
Frequently Asked Questions
What is an insulin-to-carb ratio and how is it determined?
The insulin-to-carb ratio (ICR or I:C ratio) tells you how many grams of carbohydrates are covered by one unit of rapid-acting insulin. A ratio of 1:10 means one unit of insulin covers 10 grams of carbohydrates. Your endocrinologist determines this ratio based on your individual insulin sensitivity, which is influenced by factors like body weight, physical activity level, and degree of insulin resistance. A common starting estimate uses the 500 Rule: divide 500 by your total daily insulin dose to get the approximate grams of carbs covered per unit. ICR can vary throughout the day, with many people needing more insulin per carb in the morning due to dawn phenomenon and insulin resistance patterns.
What is a correction factor and how does it work?
The correction factor (also called insulin sensitivity factor or ISF) tells you how much one unit of rapid-acting insulin will lower your blood glucose, measured in mg/dL. For example, a correction factor of 50 means one unit of insulin will drop your blood glucose by approximately 50 mg/dL. It is commonly estimated using the 1800 Rule for rapid-acting insulin: divide 1800 by your total daily insulin dose. For regular insulin, the 1500 Rule is used instead. Like the insulin-to-carb ratio, the correction factor varies between individuals and can change throughout the day. Your healthcare team will fine-tune this number based on your blood glucose response patterns over time and through careful testing.
What is insulin on board and why does it matter for dose calculations?
Insulin on board (IOB), also called active insulin, is the amount of previously administered rapid-acting insulin that is still working in your body. Rapid-acting insulin like Humalog, Novolog, and Fiasp have a duration of action of approximately 3-5 hours, with peak effect at 1-2 hours. Accounting for IOB prevents insulin stacking, a dangerous situation where multiple correction doses overlap and cause severe hypoglycemia. Modern insulin pumps automatically track IOB, but people on multiple daily injections must manually estimate it. A general approximation is that about 20% of the dose is used per hour, so 3 hours after a 5-unit dose, approximately 2 units remain active.
How do I calculate insulin doses for mixed meals with protein and fat?
Traditional bolus calculations focus on carbohydrates because they have the most immediate impact on blood glucose. However, protein and fat also raise blood glucose, just more slowly and to a lesser extent. Protein converts to glucose at approximately 50-60% efficiency over 3-5 hours, and fat can delay carb absorption and cause sustained glucose elevation for 4-8 hours. For high-protein meals, some clinicians recommend adding 50% of protein grams to the carb count for dosing. For high-fat meals like pizza, a dual-wave or extended bolus on an insulin pump delivers part of the dose immediately and the remainder over 2-4 hours. Discuss these advanced dosing strategies with your diabetes care team.
What blood glucose target should I use for my calculations?
Blood glucose targets vary based on individual circumstances and should be set by your healthcare provider. The American Diabetes Association recommends a premeal target of 80-130 mg/dL for most adults with diabetes. Post-meal targets are typically below 180 mg/dL measured 1-2 hours after eating. Some providers set tighter targets of 100-120 mg/dL for patients using continuous glucose monitors who have low hypoglycemia risk. Pregnant women with diabetes typically have tighter targets of 60-95 mg/dL fasting and below 120 mg/dL one hour after meals. Older adults or those with hypoglycemia unawareness may have relaxed targets of 100-150 mg/dL to prioritize safety over tight control.
What are the risks of incorrect insulin dosing?
Incorrect insulin dosing carries significant health risks in both directions. Too much insulin causes hypoglycemia (low blood sugar below 70 mg/dL), which can progress from mild symptoms like shakiness and sweating to severe complications including confusion, seizures, loss of consciousness, and in extreme cases, death. Too little insulin results in hyperglycemia, which if sustained leads to diabetic ketoacidosis (DKA) in type 1 diabetes, a life-threatening emergency. Chronic underdosing accelerates long-term complications affecting eyes, kidneys, nerves, and cardiovascular system. Common dosing errors include miscounting carbohydrates, forgetting to account for insulin on board, using the wrong ratio at different times of day, and not adjusting for exercise.
How does exercise affect insulin dosing requirements?
Exercise significantly impacts insulin sensitivity and glucose uptake, requiring dose adjustments to prevent hypoglycemia. Aerobic exercise like walking, running, or cycling increases insulin sensitivity for up to 24-48 hours and can cause blood glucose to drop during and after activity. Most people reduce their meal bolus by 25-50% for meals before or after moderate exercise. Vigorous exercise or anaerobic activities like weight lifting may initially raise blood glucose due to stress hormones, then cause delayed drops hours later. Strategies include reducing basal insulin before exercise for pump users, consuming extra carbohydrates without bolusing, or both. Exercise timing, intensity, duration, and individual response all influence the optimal dosing adjustment.
How do insulin doses differ between type 1 and type 2 diabetes?
Type 1 diabetes requires all insulin from external sources since the pancreas produces none, typically totaling 0.5-1.0 units per kilogram of body weight per day split between basal and bolus doses. Type 2 diabetes often starts with oral medications and lifestyle changes, with insulin added when needed. Type 2 insulin doses are often higher due to insulin resistance, sometimes exceeding 1-2 units per kilogram daily. The insulin-to-carb ratio is typically more aggressive (lower numbers like 1:5 or 1:8) in type 2 due to resistance, while correction factors are also smaller (meaning more insulin needed per mg/dL correction). Concentrated insulins like U-200 and U-500 exist specifically for type 2 patients requiring large doses.
What is the difference between basal and bolus insulin?
Basal insulin provides a constant low-level background insulin to manage glucose produced by the liver between meals and overnight, typically covering about 50% of daily insulin needs. Long-acting insulins like Lantus (glargine), Levemir (detemir), and Tresiba (degludec) are injected once or twice daily and have durations of 12-42 hours depending on the type. Bolus insulin, also called mealtime insulin, is rapid-acting (Humalog, Novolog, Fiasp) taken before meals to cover carbohydrate intake and correct high blood sugar. Bolus insulin begins working within 10-20 minutes and peaks at 1-2 hours. Insulin Dose Calculator focuses on bolus insulin dosing, which requires precise calculation based on current glucose, carb intake, and correction needs.
Should I adjust insulin doses when I am sick?
Illness frequently increases blood glucose levels due to stress hormones like cortisol and glucagon, often requiring increased insulin doses even when eating less. The standard sick-day guideline is to never skip basal insulin, check blood glucose every 2-4 hours, and test for ketones if glucose exceeds 240 mg/dL. Correction doses may need to be given more frequently, and some providers recommend reducing the correction factor by 20-30% during illness (meaning giving more insulin per glucose point). If vomiting prevents eating, mini-doses of glucagon can prevent hypoglycemia while maintaining insulin coverage. Specific sick-day insulin adjustment plans should be established with your endocrinologist in advance. Contact your provider if glucose remains above 300 mg/dL or if moderate to large ketones are present.
References
Reviewed for accuracy by Rahul Singh, Health & Wellness Specialist · Editorial policy
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