Bolus Calculations (Part I)

Think Like a Pancreas: Chapter 7, Your Cheat Guide!   (Part I)

I don't know about you, but calculating is not my forte. 

Before having Type 1, I was a free bird and whimsically ate whatever the heck I wanted. I still ate pretty clean back then, but I would eat an entire watermelon or grab a few crispy crunchy chocolate chip cookies whenever I wanted. *Sigh* 

Sure, I can still eat those things, but this disease has taught me mindfulness on what foods do what to my body and excess sugar intake is the root of many illnesses and disease. So cheers to healthier living thanks to Type 1. ;)

Okay, let's dive into Chapter 7.

Bolus Calculations

Boluses are bunches of rapid acting insulin used to cover carbs or lower high blood sugar levels. 

Four Factors that are used to determine bolus dose:

  1. the amount of carbohydrate in a meal or snack
  2. the blood sugar level at the time of a meal or snack
  3. the amount of insulin still remaining from previous boluses
  4. the amount of planned (or completed) physical activity. 

Part I. Insulin to Cover Carbs

To determine how many grams of carbohydrates each unit of rapid acting insulin covers we use the “insulin to carb ratio (I:C).”

Example: A “1:10 ratio” means that one unit of insulin covers 10 grams of carbs, and a "1:20" ratio means that each unit injected covers 20 grams. To figure out your I:C ratio, simply add up the grams of carb in your usual meals and divide the units of rapid acting insulin. 

Example: If you enjoy 30 grams of carb for breakfast, divide this by (your normal dose) 3, which = 10, so it appears that each unit of insulin covers 10 grams of carb. 

The I:C ratio gives you flexibility to accurately account for as much or as little carb as you choose, but you still must be mindful of spacing meals and snacks a few hours apart.

The more you snack, the less control you are likely to have because it keeps you in a perpetual state of blood sugar rise versus allowing for the bolus to kick in and normalize your blood sugars. 

Your I:C CAN VARY. Many people find that their highest bolus need is at breakfast (due to hormones), and lowest in the middle of the day (due to increased activity). 


Using Your Weight I:C Method:

This approach is based on the fact that insulin sensitivity diminishes as body mass increases…i.e. each unit of insulin will cover less food in a heavier person than lighter. 

First, divide 1,800 by your weight in pounds. For me, its 1800/145 = 12.41

This translates to 1:12

While this method is generally effective, it does not account for the variables that affect insulin response such as age (hormone production) and insulin sensitivity (how healthy and/or active you are).

Again, keep in mind, your I:C will vary. 


Fine Tuning Your I:C Ratio:

Trial and adjustment is necessary as you fine tune. 

To help with accuracy, be mindful of certain factors that can/will affect your blood sugar levels such as: major emotional stress, start of menstrual cycle, after a low blood sugar, unknown carb content (eating out), high fat meals. Each of these can skew your numbers and affect your average data. 

  • First, check your blood sugar (pre-meal) and log your number. 
  • Second, log the amount of carbs consumed & bolus given.
  • Third, check your blood sugar (post-meal) three hours later, without taking in any calories or bolus insulin in between. 
  • Attempt this process for at least one, or even two weeks to fine tune your I:C ratio.

Considering this is diabetes , and nothing can be simple (WHYYY?!), your numbers could not all be consistent, but you should see a trend fur sure. 

See Table 7-3 for visual example:


Part II. Correcting your blood sugar

When correcting your blood sugar, you must first determine:

  • Your current blood sugar level
  • Your target blood sugar level
  • Your sensitivity factor (how much each unit of insulin is expected to lower your blood sugar). Stress, surgery, inflammation, pregnancy, growth, etc. are each variables that affect your sensitivity to insulin. 

Gary recommends the 1700 (94) rule for figuring out your correction ratio/sensitivity factor.  

Take your total daily insulin (including basal and bolus) and divide into 1700 (94 if measuring blood sugar in mmol/1). 

Let’s say you are taking 50 units daily (on average): 1700/50= 34 (94/50 = 1.88)

This would translate to every unit of rapid acting insulin should lower your blood sugar approximately 34mg/dl or 1.88 mmoI/1

Example: If your target blood sugar is 120, you should add one full unit for ever 34 points over 120 you are, and subtract 1 unit for every 34 points below 120. 

Formula: In mg/dl: (current blood sugar—120)/34

If your blood sugar was 250, it would be: (250—120)/34    Which would translate to needing 3.8 units of insulin to correct your blood sugar to the goal of 120. 

If your blood sugar was 100, it would be: (100—120)/34     Which would translate to taking away .5 units from your meal dose to avoid a low. 

See Table 7-4 for estimating your sensitivity factor based on your total daily insulin:


Lots of numbers. I know. I warned you. 

I would be lying if I said I used these calculations religiously when it comes to dosing and correcting. 

Like I mentioned before, I am a free bird at heart and I generally live some-what whimsically when it comes to my dosing. I am able to get away with this because I am injecting minimally (3-5 units on average per meal for low carb), which = minimal variabilities. 

That being said, I am logging and practicing these calculations all week! 

With love,