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Insulin Formulas

The insulin start formulae below may be based on basal bolus insulin therapy (BBIT at ), Diabetes Canada Guidelines or accepted practice. 

Basal Insulin Start

When basal insulin is added to non-insulin antihyperglycemic agents consider:

Diabetes Canada Guidelines: 10 units to start (individualized)

Conservative BBIT Guideline (DCC): 0.1 to 0.2 units/kg = units basal insulin
(e.g. approx. half of BBIT's most conservative TDD 0.3-0.5 u/kg, rounded down for ease)

  • E.g. 100.0 kg X 0.1 or 0.2 = 10-20 units starting basal dose 100 kg client
  • Tip: Take weight in kg and move decimal to the left for the LOWEST starting dose.
    Double that number for the HIGHEST starting dose.

Additional Basal Insulin Comments:

  • Actual needs can be significantly higher, particularly in those who are resistant, start conservatively
  • Consider starting with half the calculated dose for those with advanced renal disease
  • Occasionally, when using insulin detemir or glargine u100, the addition of another basal dose (e.g. morning), may be needed when fasting blood sugars are close to target but  supper and HS readings are significantly elevated, and no bolus insulin is currently used. There is currently no standardized formula for the addition of a second basal insulin dose. However, an accepted method is to calculate the second basal dose as slightly less than half of the current basal dose (depending on weight, glucose levels, etc.) Example: Jack is on 30 units of intermediate insulin at night. The educator requests an order for 13 units for the morning based on current blood glucose patterns.

To Adjust Basal Insulins: See Insulin Adjustment Page


Bolus Insulin Start

Diabetes Canada Guidelines: 2 - 4 units per meal

Conservative BBIT Guidelines (DCC): 0.05 - 0.1 units / kg = units per meal 

  • E.g. 100.0 kg X 0.05 or 0.1 = 5 -10 units
  • Tip: Take weight in kg and move decimal to the left for the HIGHEST starting bolus dose per meal. Cut this in half for the LOWEST starting bolus dose per meal. 
  • When to start bolus: If on > 0.5 units basal insulin per kg and not at target, consider adding bolus soon (consider A1c, age, complexity, etc).
  • Actual bolus needs can be significantly higher, particularly in those who are resistant, however start conservatively. 

To Adjust Bolus Insulins: See Insulin Adjustment Page

Basal & Bolus Start 

  • Starting TDD = 0.5 - 1.0 units/kg/day
    (0.3 - 0.5 u/kg/day if more sensitive to insulin; 0.5 - 1.0 u/kg/day if more insulin resistant)
    • Daily basal insulin =  50% of TDD 
    • Daily bolus insulin =  50% of TDD  (distributed amongst 3 meals)
    • Or, if mixed insulin (e.g. 30/70) loosely 2/3 of TDD premix at breakfast and 1/3 at supper.
  • Tip: If resistant consider this shortcut:
    • half the weight in kg = total daily basal units
    • half the weight in kg = total daily bolus units (distribute over 3 meals)
  • Example for 100 kg resistant patient
    • 50 units basal
    • 50 units bolus
      (50 / 3 meals = 16 units per meal but preferable to individualize.
      e.g. if breakfast is small and supper large, then distribute it proportionately)
  • To adjust for BBIT patterns (lows,highs,erratic) see Insulin Adjustment page.

Assessing % Basal in BBIT

  • Total daily units basal / total daily units all insulin x 100 = % of insulin as basal
    e.g. 45 units basal for the day / 90 units TDD x 100 = 50% of insulin as basal
  • For most people, approximately 40-60% of their total daily dose of insulin (TDD) is basal insulin. This split varies for those on partial-closed-loop insulin pumps due to algorithms. For those with low carbohydrate diets, expect a higher % basal.

Insulin Sensitivity Factor (ISF) or Correction Dose 

To create an ISF for RAPID insulin:

  • 100/TDD = number of mmol/L 1 unit rapid will lower glucose level.
    E.g. 100/50 units TDD = 2
    1 unit will drop glucose by about 2 mmol/L
  • *Note: If the forumula suggests ISF <2, consider ISF of 2 to start (it's safer). Fine tune later. 

To create an ISF for REGULAR insulin:

  • 83/TDD = number of mmol/L 1 unit regular insulin will lower glucose level.
    E.g. 83/30 units TDD = about 3.
    1 unit will lower glucose by about 3 mmol/L

To use an ISF:

  • (Current Blood Glucose – target) / ISF= units to give to correct high glucose reading
  • e.g. If current BG 13 mmol/L , ISF is 2 and target is 7 mmol then:
    13 mmol/L - 7 mmol/L  = 6 / ISF 2 = 3 units for correction 


Carb Ratio (formerly termed Insulin to Carb Ratio or ICR)

A Carb Ratio describes the amount of carbohydrate “covered” by one unit of bolus insulin. For example, a Carb Ratio of 10 means that each 10 g of available carbohydrate consumed (carbohydrate minus fibre) requires 1 unit of bolus insulin. 

Many of us will be familiar with the previous term, insulin-to-carbohydrate ratio (ICR). A Carb Ratio of 10, is equivalent to an ICR of 1:10 [1 unit of bolus insulin per each 10 g available carbohydrate consumed]. 


To create a Carb Ratio:

  • Method 1: Divide grams of available carbohydrate eaten for a meal by bolus dose (units) per same meal to determine the carb ratio
    e.g. 70 g available carb eaten / 5 units rapid = 14. So Carb Ratio 14
    Therefore, for every 14 g available carb eaten, 1 unit of bolus insulin is given

  • Method 2: The 500 rule (500/TDD)
    e.g. 500 / Total Daily Dose of insulin of 50 units = 10. So Carb Ratio = 10
    Therefore, for every 10 g available carb eaten, 1 unit of bolus insulin is given

  • For adjusting ICR, visit Adjusting Insulin Page

Using a Carb Ratio to calculate Insulin

When deciding how much bolus insulin to give for a meal, add up the total available carbohydrate being consumed, and divide by the Carb Ratio. Add a correction dose (as described above) if needed. For example:

  • If glucose reading is in target (so no correction is needed), the Carb Ratio is 10, and consuming 80 g carb:
    • 80/10 = 8 units bolus insulin is given