How to Calculate Your Insulin Dose Correctly?

Insulin therapy is complex, and determining the correct dosage can be challenging. Many factors must be considered when calculating your insulin dose, including the type of insulin, your blood glucose level, the amount of carbohydrates in your plate, and individual factors.
 
In this article, we will explore how to calculate basal and bolus insulin doses, taking into account individual factors such as insulin sensitivity and carbohydrate intake.
 
But keep in mind that we can only give general examples that may not apply to you. You must work closely with your healthcare provider to determine the appropriate insulin doses for your specific individual situation.
 
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How to Calculate Your Insulin Dose?

The amount of insulin to take depends on several factors, including the type of insulin being used (basal or bolus), body weight, insulin sensitivity, blood glucose level, and carbohydrate consumption in your meal.
 
Appropriate insulin dosage must be determined by a healthcare professional, who will consider your individual needs and circumstances after running a series of tests.
 
Depending on your situation, your healthcare professional may recommend different methods to calculate your insulin doses, such as the Total Daily Dose (TDD), Carbohydrate Counting, or Blood Glucose Correction Factor method.
 
Always follow your doctor’s recommendations regarding insulin therapy and monitor your blood glucose levels regularly to ensure they are within the target range. Any changes to insulin dose should be made in consultation with a healthcare professional.
 
Warning: the calculations presented below are for general examples only and may not apply to your individual insulin needs. Working with your healthcare provider to determine the appropriate insulin dose for your specific situation is crucial. Injecting insulin without knowing your correct dose can be dangerous, so never inject insulin if you aren’t sure how many units you should take.
 
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How to Calculate Your Total Daily Insulin Dose (TDD)

The Total Daily Insulin Dose (TDD) is the total amount of insulin you need per day to keep your blood glucose levels within the recommended range.
 
Typical blood sugar targets for people with diabetes are 80 to 130 mg/dL before a meal and less than 180 mg/dL two hours after a meal.
 
Here’s a general calculation to determine your body’s daily insulin requirement (total daily insulin dose):

1. Convert your weight from pounds to kilograms. To do this, divide your weight in pounds by 2.2. For example, if you weigh 150 pounds, divide 150 by 2.2 to get 68.18 kilograms.

2. Determine your recommended insulin dose per kilogram of body weight. The recommended range is usually between 0.5-1.0 units of insulin per kilogram of body weight per day. The exact dose will depend on your individual needs and circumstances. Ask your doctor for advice here.

3. Multiply your weight in kilograms by the recommended insulin dose per kilogram of body weight. For example, if your recommended insulin dose is 0.6 units per kilogram of body weight per day and you weigh 68.18 kilograms, multiply 0.6 by 68.18 to get 40.91 units of insulin per day. 

Remember that this is a general calculation formula. You may need more or less insulin than the number you obtain. For example, a higher insulin dose may be required if your body is highly resistant to insulin. In contrast, a lower insulin dose may be needed if your body is very sensitive to insulin.
 
Additionally, the TDD method is just one method for calculating insulin dose. Your healthcare professional may recommend a different approach based on your needs and circumstances.
Make sure to ask your doctor for advice.
 
Once you’ve calculated your total daily insulin dose, you must determine your basal/background dose and bolus insulin doses for each meal.

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How to calculate your basal/background insulin dose

The basal/background insulin dose typically makes up 40-50% of your total daily insulin dose.
 
For example, if your total daily insulin dose is 40 units, your basal/background insulin dose would be 16 to 20 units of either long-acting insulin (such as glargine or detemir) or rapid-acting insulin if you are using an insulin pump (continuous subcutaneous insulin infusion device).
 
The rest should be adjusted and divided into several bolus, rapid-acting insulin injections covering your meals, carbohydrate intakes, and high blood sugar corrections.
 
Related article: A Step-by-Step Guide to Using Insulin Pens for Injections.
 

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How to Calculate Your Bolus Insulin Dose

The bolus insulin dose you should inject for a meal depends on several factors, including your insulin-to-carb ratio, carbs on your plate, and high blood glucose correction factor.

How to calculate your insulin-to-carbohydrates ratio

The insulin-to-carbohydrate ratio (ICR) is the amount of insulin your body needs to cover a certain amount of carbohydrates you eat. In other words, the ICR answers that question: how many grams of carbohydrates are covered by 1 unit of insulin?
 
There are two ways to calculate your insulin-to-carb ratio:
 
Method 1. 500 ÷ Total Daily Insulin Dose
 
The ICR can be calculated using the general rule of “500”. So, in our example, if your total daily insulin dose is 40 units, your insulin-to-carbohydrate ratio would be 500 ÷ 40 = 12,5 (1:12,5).
 
It means that one unit of insulin covers 12,5 grams of carbohydrates. If you’re eating a meal that contains 60 grams of carbohydrates, you would need to inject 4,8 units of insulin (60 ÷ 12,5).
 
Method 2. Determine your initial insulin-to-carbohydrate ratio
 
While the above method provides a general rule, calculating your specific insulin-to-carb ratio with the help of your healthcare provider is absolutely essential. Indeed, people with diabetes have different ICR.
 
ICR is typically between 1:10 and 1:20, meaning one unit of insulin is needed to cover 10-20 grams of carbohydrates. Yours may be 1:12 or 1:18. While the difference seems very small, it can significantly impact your blood glucose levels.
 
Only your healthcare provider can help you determine your insulin-to-carb ratio.
 
Additionally, the example above presupposes you have a uniform insulin sensitivity over a day. But actual insulin response may fluctuate throughout the day. The same person can be insulin-resistant in the morning and insulin-sensitive in the evening. The insulin-to-carb ratio would not be the same for breakfast and dinner.
 
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How to calculate your bolus insulin dose for a meal

Calculating the bolus insulin dose for a meal depends on your insulin-to-carb ratio and the amount of carbohydrates in your meal. To calculate your mealtime fast-acting dose of insulin:

1. Determine the amount of carbohydrates in your meal: This can be done by reading the nutrition label or using a food tracking app to estimate the meal's carbohydrate content. 

2. Multiply the number of grams of carbohydrates by your insulin-to-carbohydrate ratio. For example, if you eat a meal with 50 grams of carbohydrates and your insulin-to-carbohydrate ratio is 1:10, you would need 5 units (50 divided by 10).

 
Note: this chart is for illustrative purposes only and should not be used as a substitute for medical advice. Your healthcare provider can help you determine your individual insulin-to-carbohydrate ratio and bolus insulin dose. Additionally, other factors such as your blood glucose level before a meal, physical activity, and stress can affect insulin needs, so you may need to adjust your insulin dose accordingly.
 
Related article: How to Convert Insulin Units to mL?

How to adjust insulin dose with the high blood sugar correction factor

Next, to calculate your bolus insulin dose, you must check your blood sugar level before the meal and apply a high blood sugar correction factor.
 
The high blood glucose correction factor, also known as the insulin sensitivity factor (ISF)or correction factor, is the amount of insulin needed to lower blood glucose by a certain amount.
 
It is a personalized value that is determined by your healthcare provider based on your individual insulin sensitivity and other factors.
 
For example, if your correction factor is 1:50, it means that 1 unit of insulin will lower your blood glucose by 50 mg/dL. So, if your blood glucose level is 200 mg/dL and your target is 100 mg/dL, you would need to take 2 units of insulin to bring your blood glucose down to the target level (200-100=100, 100/50=2).
 
Individual correction factors can vary over time due to factors such as changes in insulin sensitivity, physical activity, stress, illness, and medications. Therefore, you must consistently work with your healthcare provider to adjust it to maintain your target blood glucose levels.
 
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Calculate your total bolus insulin dose

To get the total mealtime insulin dose you should inject, you must add the high blood sugar correction insulin dose to your carbohydrate coverage dose.
 
For example, if your meal contains 40 grams of carbohydrates and your insulin-to-carb ratio is 1:10, your carbohydrate coverage dose is 4 units. But if your blood sugar level is 200 mg/dL and your correction factor is 1:50, you need 2 additional units of insulin. So, your total bolus insulin dose would be 4+2 = 6 units.
 
Remember: miscalculating insulin doses can be dangerous and lead to serious health complications, including hypoglycemia (low blood sugar) or hyperglycemia (high blood sugar). Therefore, it's essential to work closely with your healthcare provider to determine your insulin-to-carb ratio, total daily insulin dose, and correction factor.
 
We hope this article has helped you understand how to calculate your insulin dose. What about you? How do you calculate your insulin dose? How much insulin do you take?