How do I calculate how much insulin to take?

In people who do not have diabetes, their bodies release insulin in response to the foods they eat. This is because many foods contain carbohydrates. Some examples include bread, sweets, fruits, and even vegetables.

Your body breaks carbohydrates down into smaller building blocks, like glucose. You need insulin to use this glucose for energy. If your body cannot make or use insulin effectively, you’ll need to inject it to process your food for energy.

Calculating how much insulin to take is usually based on two considerations:

• Basal insulin dose. A basal insulin dose is an amount that you give yourself daily regardless of the foods you eat.
• Bolus insulin dose. A bolus insulin dose helps correct or anticipate the carbohydrates you eat throughout the day. You will usually correct this with a bolus dose of rapid-acting insulin.

Calculating a bolus dose is where insulin administration can get tricky. When you give yourself insulin, you are estimating how many units of insulin it will take to process the carbohydrates you eat.

The University of California, San Francisco states that, as a general rule, 1 unit of rapid-acting insulin will process anywhere from 12 to 15 grams of carbohydrates.

A bolus dose may also be used to correct high blood sugar. In general, 1 unit of insulin lowers your blood sugar by about 50 milligrams per deciliter (mg/dL).

Since the human body is so complex, not all people will process insulin the same way. Factors like time of day, stress levels, and physical activity can make these numbers more difficult to predict.

Because of this, you’ll probably start off giving yourself insulin based on numbers for the average person. After seeing how these numbers help you manage your blood sugar, you may have to adjust based on how your body uniquely responds to the insulin you administer.

Putting it all together

Now that you know the how and why behind insulin dosing, let’s consider how you may calculate your insulin needs.

You’ll usually give yourself an insulin dose around your meals since that’s when you take in carbohydrates. You also will typically check your blood sugar.

To calculate your insulin needs:

1. Check your blood sugar level before a meal.
   • If your blood sugar level is in your target range, you do not need to calculate for extra insulin.
   • If your blood sugar level is higher than your target range (usually around 120), calculate how much insulin you’ll need. You should talk with your doctor about this, but usually, 1 unit of fast-acting insulin will bring your levels down by 50 points.
2. Calculate the number of carbohydrates you’re about to eat. You can usually estimate these using carbohydrate counters.
   • For every 12-15 grams of carbohydrates, give yourself 1 unit of rapid-acting insulin. Ask your doctor if this number may be different for you.
3. Add the number of units needed to adjust for both your target range and meal.
4. Administer the total units of insulin.

You may find that if you generally eat about the same amount of carbohydrates each day, you may be able to consistently inject the same amounts of insulin outside of special occasions. It takes time to find out how your body best responds to insulin.