This Insulin Bolus & Correction Calculator helps estimate a mealtime insulin dose or correction dose using your current blood sugar, target blood sugar, carbohydrate amount, insulin-to-carbohydrate ratio, and insulin sensitivity factor.
Use this calculator only if your diabetes care team has already given you your personal insulin-to-carb ratio, correction factor, target range, and safety instructions.
This tool is for education and dose-estimation support only. It does not prescribe insulin and should not replace your doctor’s insulin plan.
Insulin can cause serious low blood sugar if the dose is too high, repeated too soon, or taken when you are not eating enough. Do not use this calculator to start insulin, change insulin doses, or replace a written medical plan.
Do not use this calculator if you have moderate or large ketones, vomiting, dehydration, confusion, severe weakness, chest pain, trouble breathing, or very high blood sugar with illness. Follow your sick-day plan and contact urgent medical care when needed.
Written by: Dr. Albana Greca, MD, MMedSc, Family Physician and Medical Author.
Medically reviewed by: Dr. Ruden Cakoni, MD, Endocrinologist.
Last reviewed: July 2026.
Insulin math can feel overwhelming. This calculator is designed to make the calculation easier by showing how meal carbohydrates and correction insulin are estimated. It is most useful for people who already use rapid-acting or short-acting insulin before meals.
A bolus calculator can reduce guesswork, but it is only as safe as the numbers entered into it. Your insulin-to-carbohydrate ratio, correction factor, target glucose, and insulin-on-board rules should come from your doctor, diabetes nurse, or diabetes educator. If you are still learning how insulin works, our guide to insulin treatment for diabetes explains the difference between background insulin and mealtime insulin.
Use your personal settings from your diabetes team. Educational tool; not medical advice.
If BG < 70 mg/dL, treat hypoglycemia first. If BG > 300 mg/dL, follow sick‑day/ketone protocol and contact your care team.
Enter your current blood sugar, target blood sugar, carbohydrate amount, insulin-to-carbohydrate ratio, insulin sensitivity factor, and insulin on board. Make sure all settings come from your diabetes care team.
Accurate carbohydrate counting is essential. If you are unsure how many grams of carbohydrate are in your meal, use our carb counter calculator for diabetics before estimating your meal bolus.
Use your personal settings from your diabetes team. Educational tool; not medical advice.
Current BG: mg/dL
Target BG: e.g., 110 mg/dL
Carbohydrates: e.g., 60 g
Carb Ratio: e.g., 10 g/unit
Insulin Sensitivity: e.g., 50 mg/dL per unit
Insulin on Board: rapid-acting insulin still active from an earlier dose
Safety rule: If BG is below 70 mg/dL, treat hypoglycemia first. If BG is above 300 mg/dL, follow your sick-day or ketone protocol and contact your care team.
A bolus is a dose of rapid-acting or short-acting insulin used around meals or to correct high blood sugar. Meal bolus insulin helps cover the glucose rise from carbohydrates. Correction insulin helps bring high blood sugar closer to your target range.
Basal insulin is different. Basal insulin works in the background between meals and overnight. This calculator is for bolus and correction insulin only, not long-acting basal insulin.
A common meal insulin formula is:
Meal bolus = grams of carbohydrate ÷ insulin-to-carbohydrate ratio
Example: If you plan to eat 60 grams of carbohydrate and your insulin-to-carbohydrate ratio is 1 unit for every 10 grams, the estimated meal bolus is 6 units.
Mixed meals with more fat and protein can raise blood sugar later. Some people using insulin pumps or advanced insulin plans may need a delayed or split bolus, but this should be planned with their diabetes team.
A common correction formula is:
Correction dose = (current blood sugar − target blood sugar) ÷ insulin sensitivity factor
Example: If your current blood sugar is 220 mg/dL, your target is 120 mg/dL, and your insulin sensitivity factor is 50 mg/dL, the estimated correction is 2 units.
The total estimated bolus may include both meal insulin and correction insulin. If you know your insulin on board, it may need to be subtracted to reduce the risk of insulin stacking.
If you are unsure whether a reading is mildly high, very high, or urgent, compare it with our guide to blood sugar that is too high or too low.
An insulin-to-carbohydrate ratio, or ICR, tells you how many grams of carbohydrate are covered by 1 unit of insulin. For example, an ICR of 1:10 means 1 unit of insulin covers about 10 grams of carbohydrate. An ICR of 1:15 means 1 unit covers about 15 grams.
Your ICR must be personalized. Some people need one ratio for all meals, while others need different ratios for breakfast, lunch, and dinner because insulin sensitivity changes during the day. Many people need more insulin at breakfast because of morning insulin resistance, but this varies individually.
Insulin sensitivity factor, or ISF, estimates how much 1 unit of rapid-acting insulin lowers your blood sugar. For example, an ISF of 50 mg/dL means 1 unit may lower glucose by about 50 mg/dL.
ISF is not the same for everyone. It can change with illness, stress, exercise, sleep, hormones, weight changes, kidney function, and insulin resistance. Sensitivity may also differ at night, so correction rules can vary by time of day.
Insulin stacking happens when correction doses are taken too close together while previous rapid-acting insulin is still active. This can cause delayed low blood sugar several hours later.
Many rapid-acting insulins continue working for 3–5 hours. Before taking another correction dose, follow your care team’s instructions about timing, active insulin, and insulin on board.
Tracking the time of each bolus can help prevent accidental stacking. A simple blood sugar log sheet can help you record glucose, carbs, insulin dose, activity, and symptoms.
Correction targets vary from person to person. Some people correct above 180 mg/dL, while others may have a different threshold such as 140–160 mg/dL depending on age, hypoglycemia risk, pregnancy, kidney disease, and overall glucose goals.
Many people use a target around 100–120 mg/dL, but your personal target may be different. Do not copy another person’s correction factor or target blood sugar. Your diabetes care team should set these numbers for you.
Because targets can change by time of day, it may help to review our guide to blood sugar levels by time of day before discussing your correction plan with your diabetes team.
It may be used for a correction-only estimate if your doctor has told you how to correct high blood sugar without eating. In that case, you would enter zero carbohydrates and use only your correction factor.
However, correction-only dosing can increase hypoglycemia risk if you recently took insulin, exercised, drank alcohol, are ill, stressed, inactive, or eating less than usual. Avoid repeated corrections too close together.
It is normal for an insulin calculator to give different results from one day to another because your body is not the same every day. Stress hormones, illness, infection, poor sleep, activity, and hormonal changes can all increase or reduce insulin sensitivity.
Even if you eat the same food, your insulin needs may differ. This does not mean the calculator is wrong. It reflects real biological changes and helps you discuss patterns with your care team.
Children, teenagers, and older adults can use an insulin calculator only with extra caution and supervision. They may need smaller, more precise doses, and rounding errors can significantly affect blood sugar.
People with type 2 diabetes who use rapid-acting mealtime insulin may also use a bolus calculator. Bolus insulin is not only for type 1 diabetes. The key is that all settings must be individualized and prescribed by a healthcare professional.
An insulin calculator can reduce guesswork, but it is only as safe as the settings entered into it. Your insulin-to-carb ratio, correction factor, target range, insulin timing, and sick-day plan should come from your diabetes care team and should be reviewed when your glucose patterns change.
Educational safety note: This calculator and page are for general diabetes education only. They do not replace personal medical advice, diagnosis, or treatment. Do not start, stop, or change insulin doses, insulin pump settings, diabetes medicines, correction factors, carbohydrate ratios, diet, or exercise without speaking with your healthcare provider.
It can support safer calculations only if you enter insulin settings prescribed by your diabetes care team. It is not safe to guess your ratios or copy another person’s insulin plan.
Yes, if you have type 2 diabetes and use rapid-acting mealtime insulin. It is not for people who do not use bolus insulin.
No. This calculator is for bolus and correction insulin. It should not be used to calculate long-acting basal insulin doses.
Do not take a dose that feels unsafe. Recheck your inputs, confirm your blood sugar, consider active insulin, and contact your diabetes team if unsure.
If your blood sugar is below 70 mg/dL, follow your low blood sugar treatment plan. Many plans use 15 grams of fast-acting carbohydrate, wait 15 minutes, and recheck.