Insulin Calculation

Submitted by Thiruvelan on Fri, 04/19/2013

Insulin calculation formula in this page is the generalized rule for find daily insulin dosage both basal and bolus requirement. However, bear in mind your insulin requirement can be lower if you are newly diagnosed and still making insulin on your own and requirement is higher if you are very resistant to insulin. Monitor your BS; vary your insulin requirement for the best insulin dose to meet your individual needs.

How do you do the insulin calculation?

The insulin requirements for type 1 diabetes cannot calculate precisely because every individual is different. However, to begin the treatment, there is a simple thumb rule formula exist, which can help you provide just close to your insulin requirement. After by trial and measurement, you can fine-tune your insulin treatment. 

Before proceed further, you should learn some important term in your insulin calculations, they are:

  • Total daily dose of insulin is the insulin requirement of both basal and bolus insulin.
  • The basal insulin (background insulin) is the insulin requirement; overnight, during fasting and in-between meals.
  • The bolus insulin is the insulin requirement to cover the mealtime carbohydrate and blood sugar correction.
  • Insulin to the carb ratio is the grams of carbohydrate the body can dispose by one unit of insulin.
  • CHO insulin dose is the insulin requirement to cover the total grams of carbohydrate.
  • Insulin sensitivity factor or Blood sugar correction factor is defining, as one unit of insulin (rapid acting) will drop the blood-sugar level
  • Blood sugar insulin correction dosage is the insulin requirement to cover the blood sugar deviation from the target.
  • Total mealtime bolus insulin is the insulin requirement to cover the mealtime carbohydrate and deviation in the blood sugar. 

Calculate your total daily insulin dose

Every individual body is different and thus their insulin requirement is distinct; YMMV is an acronym stands for "Your Mileage May Varies." Therefore, you need to do some trial to find out your exact total daily insulin dose requirement.

To begin with, there is a thumb rule formula to roughly estimating your total daily dose (TDD) of insulin requirement.

TDD = Body weight (in lbs.) x 0.25 (or) Body weight (in Kg.) x 0.55

For example, If your body weight is 140 pounds, then your total daily insulin dose = 144 x 0.25 = 35 units of insulin.

Calculate your basal & bolus insulin dose

Is it the time to start Basal/Bolus Insulin regimen? Do you want to tighten your blood-glucose level then basal bolus insulin regimen is your choice? Basal provides sufficient insulin throughout 24 hours to cover a base requirement with intermediate or long acting insulin’s (NPH, Lente, Ultralente, and Lantus) at bedtime or sometimes before. Bolus provides an insulin requirement to cover the glycemic effect of meals with rapid acting insulin (Regular, Humalog, and NovoLog). Bolus insulin dosage covers your carbohydrate during meal’s time and high blood sugar correction.

  • Basal insulin dose = 40 to 50% of TDD (total daily dose of insulin)
  • Bolus insulin dose = 50 to 60% of TDD (total daily dose of insulin)

For example, Once your total daily insulin requirement is 35 units of insulin then; Your basal insulin dose = 35 x 40 (to 50)/100 = 14 to 17.5 units of insulin. Your bolus insulin dose = 35 x 50 (to 60)/100 = 17.5 to 21 units of insulin.

Calculate insulin to the carbohydrate ratio

The I:C ratio give you an idea to know how much insulin you need for a bolus dose to help your body to metabolize the quantity of carbohydrate you will be consuming in a meal or a snack. 500 or 450 rule is in use to calculate I:C ratio.

  • I:C ratio (Regular) = 450 / TDD
  • I:C ratio (Humalog & Novolog) = 500 / TDD

For example, if yours total daily insulin dose is 35 units of insulin, then; for Humalog & Novolog insulin users: 500/35 = 14.28 (one-unit insulin moves 14 grams of carbohydrates) and for Regular insulin users: 450/35 = 12.85 (one-unit insulin moves 13 grams of carbohydrates).

Calculate the insulin requirements to cover the carbohydrate

Measure the carbs in your meals correctly. Then you can calculate the insulin requirements to cover this carbohydrate using the below formula.

Insulin to cover the carbohydrate = Grams of carb/I:C ratio (insulin to carb ratio).

For example, if your meal time carbohydrate is 50 grams, then your insulin (Humalog & Novolog, I:C ratio 14.28 from previous calculation) requirement to cover the carbohydrate = 50/14.28 = 3.5 units for regular insulin (I:C ratio 12.28) = 50/12.28 = 4 units of insulin to cover 50 grams of carbohydrate.

Calculate the blood sugar correction factor (Insulin sensitivity factor)

When your blood-glucose level goes high, a correct amount of bolus can help to bring it back to normal. To calculate correction bolus, you require determining your correction factor.

To calculate the correction factor, there are two rules 1500 (for Regular insulin) and 1800 (for Humalog and Novolog insulin - some even prefer to use a 2000 rule for this insulin) are in use.

  • BS correction factor (Regular) = 1500 / TDD mg/dl
  • BS correction factor (Humalog & Novolog) = 1800 / TDD mg/dl

For example, once your total insulin dose is 35 then your correction factor (for regular insulin) = 1500/35 = 43 mg/dl of BS drop for a unit of insulin and your correction factor (for humalog or novolog) = 1800/35 = 51 mg/dl of BS drop for a unit of insulin (or some prefer to use 2000/35 = 57 mg/dl).

Calculate the BS correction insulin dose

When your blood-glucose level goes high, a correct amount of bolus can help to bring it back to normal.

BS insulin correction dose = (Actual BS - Target BS) / BS correction factor

For example, if the present blood sugar number is 200 mg/dl and your target is 110 mg/dl, then BS insulin (Regular insulin sensitivity factor 43 mg/dl from previous calculation) correction dose = (200-110)/43 = 2 units and for Humalog or Novolog insulin sensitivity factor of 51 mg/dl = (200-110)/51 = 1.8 units.

Calculate total mealtime bolus insulin-dose

Finally, to get the total mealtime insulin dose, you have to add the insulin required to cover carbohydrate in meals and BS correction insulin-dose.

Total mealtime bolus insulin = carbohydrate insulin dose + BS correction insulin dose

For example, for Humalog & Novolog, the carbohydrate insulin dosage is 3.5 units (from previous calculation), BS correction insulin 2 units and for regular insulin, the carbohydrate insulin dosage is 4 units, and BS correction insulin is 1.8 units. Total mealtime bolus insulin = 3.5 + 2 (Humalog & Novolog) = 5.5 units or 4 + 1.8 (Regular) = 5.8.


Are you panic about mathematics like me? Do not worry, there is a "Insulin dose calculator" for you to simplify your job. Just enter few details, then you will be presented with your insulin requirement result.