Insulin Dosage Calculator

What meal bolus arithmetic represents

A meal bolus may include insulin for carbohydrate plus insulin intended to correct glucose above an agreed target. The insulin-to-carbohydrate ratio states how many grams of carbohydrate one unit is prescribed to cover. A ratio written 1:10 means one unit for 10 g carbohydrate. The insulin sensitivity factor states the expected glucose reduction from one unit.

These settings are prescriptions, not population constants. They can differ by time of day and change with insulin sensitivity, pregnancy, puberty, kidney function, illness, activity, and other medicines. A diabetes care team establishes the ratio, correction factor, target, rounding rule, and timing for a specific person and insulin.

This calculator demonstrates arithmetic after those prescribed settings are entered. It cannot verify that the settings are current or safe.

Its displayed total is not a dose recommendation and must not be used instead of an individualized written plan, pump, smart pen, or clinician instruction.

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Exact formula used by this calculator

Carbohydrate component = grams of carbohydrate / grams covered by one unit. Correction component = maximum of zero and [(current glucose − target glucose) / insulin sensitivity factor]. Displayed total = carbohydrate component + correction component. All glucose values and the sensitivity factor must use the same unit system.

The maximum-of-zero rule means this tool never subtracts insulin when current glucose is below target. A clinical plan may call for a reduced meal dose, treatment of hypoglycemia, delayed insulin, or another action. Because the calculator cannot perform that logic, a below-target input is a reason to stop and follow the prescribed low-glucose plan.

The formula does not subtract insulin on board, account for trend arrows, or check when the last bolus was given. It also does not know the insulin concentration, delivery increment, intended meal timing, or whether the carbohydrate estimate is reliable.

These omissions can make direct use unsafe.

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Worked arithmetic example

Using example settings only, 45 g carbohydrate with a prescribed ratio of 1 unit per 10 g gives 45 / 10 = 4.5 units. Current glucose 180 mg/dL, target 100 mg/dL, and a prescribed sensitivity factor of 50 mg/dL per unit give (180 − 100) / 50 = 1.6 units. The displayed arithmetic total is 6.1 units.

If current glucose were 80 mg/dL with the same target, the raw correction would be negative. This calculator sets it to zero and still displays 4.5 units from carbohydrate.

That behavior is not proof that 4.5 units is safe. A person-specific plan may require treating the low or reducing the meal component.

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Where ratios and correction factors come from

Clinicians may use total daily insulin to create a starting estimate, then revise it from observed patterns. Heuristics often called the 500 rule for carbohydrate ratio and the 1800 rule for rapid-acting insulin sensitivity appear in diabetes education, but they do not replace review of glucose data, meal timing, activity, and hypoglycemia.

The 500 rule estimates grams covered per unit as 500 / total daily insulin. The 1800 rule estimates mg/dL lowered per unit as 1800 / total daily insulin. For 40 total units per day, those estimates are 12.5 g per unit and 45 mg/dL per unit. They are starting heuristics, not settings a reader should adopt independently.

Pattern review distinguishes ratio problems from basal insulin problems, carbohydrate-counting errors, delayed digestion, and correction stacking. Recurrent post-meal highs do not automatically mean the ratio should be stronger.

Clinicians also review lows, overnight trends, injection technique, infusion sites, insulin storage, and missed doses.

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Insulin on board and correction stacking

Rapid-acting insulin continues working after the glucose-lowering effect begins. Insulin on board estimates active insulin remaining from earlier doses. Giving a full correction while substantial active insulin remains can duplicate the correction and lead to hypoglycemia later.

Pumps, automated insulin delivery systems, and some smart pens calculate active insulin using programmed duration and dose history. This page has neither. Do not copy its total into a device or syringe.

Use the bolus calculator already configured by the diabetes team when that is part of the treatment plan. The time since the last dose alone is not enough to calculate active insulin safely because action profiles differ by insulin, dose, delivery site, temperature, and person. Repeated corrections, especially when glucose is changing rapidly, require the rules in the individualized plan.

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Meal, activity, illness, and timing factors

Carbohydrate counts from labels, recipes, restaurant estimates, and portion guesses carry error. Fiber, sugar alcohols, fat, and protein can change timing. High-fat mixed meals may produce a delayed rise, while gastroparesis can make absorption unpredictable. Basic addition cannot select an extended or split bolus strategy.

Activity can increase insulin sensitivity during and after exercise, while intense activity can sometimes raise glucose temporarily. Alcohol can increase delayed hypoglycemia risk. Illness, stress, menstrual-cycle changes, and glucocorticoids can raise requirements. Kidney impairment can reduce insulin clearance and increase low-glucose risk.

Premeal timing depends on the insulin, current glucose and trend, meal, and prescribed plan. Pregnancy and pediatric care require tighter supervision and changing settings.

This tool has no inputs for those factors and should not be used to improvise an adjustment.

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Hypoglycemia safety

Glucose below 70 mg/dL is clinically important hypoglycemia. If glucose is low or symptoms suggest a low, stop the calculation and follow the personal treatment plan. ADA guidance commonly uses glucose as the preferred treatment: for a conscious person, consume fast-acting glucose, reassess after 15 minutes, and repeat if hypoglycemia continues. Individual instructions can differ.

Severe hypoglycemia is an emergency in which a person needs help because of altered physical or mental status. Glucagon should be available for people at increased risk, and family or close contacts should know where it is and how to use it. Call emergency services when the person cannot safely swallow, is unconscious, has a seizure, or does not recover as expected.

Frequent lows, overnight lows, impaired awareness, or any severe episode require prompt treatment-plan review. A clinician may need to change targets, ratios, insulin timing, delivery settings, or monitoring alerts.

Continuing to use the same arithmetic after recurrent hypoglycemia is unsafe.

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Monitoring and laboratory context

A bolus calculator manages a moment in an established insulin plan. It does not diagnose diabetes or determine whether insulin is needed. Diagnosis uses laboratory A1C or plasma glucose criteria, while insulin initiation and selection require clinical classification and education.

Current glucose may come from a meter or CGM. A CGM measures interstitial glucose and can lag during rapid change. ADA technology guidance advises access to a blood glucose meter and confirmation when the sensor reading does not match symptoms or when required by the device instructions.

Meter accuracy depends on clean hands, an adequate sample, unexpired properly stored strips, and a suitable device. A contaminated finger or unit mismatch between mg/dL and mmol/L can create a dangerous correction.

This calculator accepts mg/dL-style settings and should not receive mmol/L values unless the interface explicitly converts every glucose field and sensitivity factor.

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How to use this insulin dosage calculator

Use it only to study how the two arithmetic components combine. Enter settings copied from a current written plan: target glucose, grams covered per unit, and correction factor. Enter carbohydrate and current glucose in matching units. Compare the displayed component math with a worked example from your diabetes educator, but do not administer the displayed total.

Stop if glucose is below target, falling quickly, or inconsistent with symptoms. Also stop if there is active insulin, recent exercise, alcohol, illness, vomiting, uncertain carbohydrate, a pump or pen warning, or any doubt about the settings. Follow the prescribed plan or contact the diabetes service.

Seek urgent help for severe hypoglycemia, inability to keep fluids down, moderate or high ketones according to the sick-day plan, difficult breathing, confusion, or persistent very high glucose.

Newly diagnosed people and anyone whose regimen changed should receive hands-on education before calculating or delivering meal insulin.

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How it works

Bolus = carbs/IC ratio + (current glucose − target)/ISF. For education only. Not medical advice.

Frequently asked questions

• Can I use this instead of my doctor's plan?No. Insulin dosing must be individualized by your healthcare team. This calculator is for learning only.

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References

1. American Diabetes Association Professional Practice Committee. Glycemic Goals, Hypoglycemia, and Hyperglycemic Crises: Standards of Care in Diabetes 2026
2. American Diabetes Association Professional Practice Committee. Pharmacologic Approaches to Glycemic Treatment: Standards of Care in Diabetes 2026
3. Walsh, Roberts, and Bailey. Guidelines for optimal bolus calculator settings in adults
4. American Diabetes Association Professional Practice Committee. Diabetes Technology: Standards of Care in Diabetes 2026
5. Centers for Disease Control and Prevention. Treatment of Low Blood Sugar
6. National Institute of Diabetes and Digestive and Kidney Diseases. Low Blood Glucose (Hypoglycemia)
7. U.S. Food and Drug Administration. Blood Glucose Monitoring Devices
8. Endotext. Insulin Management of Type 2 Diabetes Mellitus