Number calculations on pump

I have a big question. Does anyone know the method of calculating how much a bolus of say, 0.8 will drop blood glucose?
Sometimes when I enter my BG and carbs I am about to eat, the pump will suggest, for example, 2.3
What is the number that is after the . multiplied by to determine how low the bolus shot will drop BG?
I have seen suggestions of 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9
My current carb ratio is 18
ISF 52
Basal rates

  1. 12 am 0.200
  2. 8 am 0.500
    One unit of insulin drops my BG 50 mg.
    I have tried googling this information and found nothing in regards to the calculation method for determining how much the number after the period will drop the BG.
    I have read that you can divide the carbs you are going to eat by your ICR-Insulin to Carb ratio, which I think in my case is my ISF-52
    Any help would be greatly appreciated, as I am bad with math!!!

Michelle @Amethyst8,
Each of us is different when it comes to “how much” a unit of insulin will drop BG. And the “insulin sensitivity factor” you have set in your pump is used in the pump algorithm.
To determine your sensitivity to a unit of insulin [and your sensitivity factor could be different at various times of day] I suggest the following method.

For safety, this should be done only when your BG is at least 150 mg/dl and you haven’t engaged in any extra-ordinary activities - i.e., your body is in “normal” mode.

  1. Check BG and write it down, should be at least 150;
  2. Bolus exactly 1 unit of the type insulin in your pump;
  3. Wait two hours and Check BG;
  4. Check BG again an hour later;
  5. YEP, Check BG again 4 hours after you took the single unit and then calculate the differences between BG readings; this should give you a pretty good sensitivity factor so pot this in your pump.

Of course, this calculation could be adversely affected if your basal rates are not properly set. Before checking my sensitivity factor, I always validate my basal rates; I’ll explain my methods for this if you need guidance.
I’m not a medical doctor, just a guy who has been intrigued while living on insulin for the past 60 years. There used to be a bunch of worksheets for pump settings on the Medtronic site.

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@Amethyst8 hi Michelle,

it depends on how many time you blink your eyes.

all kidding aside, an “accurate” bolus depends on so many things it cannot be a simple answer.

If I am active, say walking around a bit versus sitting down, the exact same bolus will have completely different affect.

So my pump came with a sensitivity of 32 default. That means that a starting point on a pump is 1.0 (one point zero) units of u100 insulin will bring your bs down 32 mg/dl in 4 (four) hours. Yours is set to 50, which means you are petite and/or very sensitive to insulin - and it means a drop of 50mg/dl in 4 hours

Pumps will always count the IOB (insulin on board) and SUBTRACT. SO lets say you bolused 4 units for a bit of ice cream, test your blood sugar at +2 hours after eating and you get a 275 mg/dl. OK you want to correct? this is called stacking insulin. Your pump will say you still have 2 units on board and suggest about 0.9 units of correction, if your sensitivity is 50 (mg u/dl) and your target blood sugar is 130 mg/dl on the high side.

so it’s current BG - high target bg (275-130 = 145 mg/dl) You have 2 units on board so that should drop your be as follows: sensitivity is 50 mg/u dl so 2 units drops your blood sugar 100 mg/dl so the 2 units on board will drop your bs 100 mg/dl of the 145 you need to drop leaving 45 gm/dl. 45/50 = 0.9 units

now that 0.9 units will either do the trick, or cause a crash (if you are very active) or do almost nothing if you are going to sleep…

please consider reading the book “pumping insulin”

good luck.

Thanks Joe for your advice, but my question really was concerning how to do the calculations for numbers such as 2.3, or 3.7, as far as how much it will drop the blood sugar. I need a method in which to do these calculations as I am bad with math.
The number after the decimal is what I am talking about. How much will that drop the blood glucose?

Hi Dennis, my real question was how to do the calculations on numbers such as 2.3 or 3.4. It’s the number after the decimal point that I don’t know how to calculate to figure how much it will drop blood sugar.
What is the formula used to calculate? What number do you times the .3 or .4 by?
I’m not trying to figure out my sensitivity factor, my endocrinologist does all this. But I have asked him about the number after the decimal point and he hasn’t given me an answer!
I thank you for your help anyway!!!

okay, your sensitivity is 50. that means 1 unit will drop your bs 50 mg/dl

0.5 units (0.5 times 50) = 25 mg/dl

0.1 units (0.1 times 50) = 5 mg/dl

2.3 units of insulin - times 50 (use a calculator, like the one on your phone if you have a smartphone or they still make small credit-card sized calculators you can buy) will drop your bs 115 mg/dl - if you wait the whole 4 hours or whatever your active insulin is set for.

if you want to go backwards… such as how many units to drop my blood sugar 147 mg/dl… then you take your drop (147) and divide by your sensitivity (50)

147 divided by 50 is 2.94 units.

the pump will mess with your head because it allows for IOB which depends on how long you set your active insulin (in hours) and your upper limit for blood sugar (target blood sugar). cheers

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Thanks so much for this new information!!! It has cleared up my confusion!!!

But on another note, my endocrinologist had me change my sensitivity to 52 and carb ratio to 18.

But you have provided the answer to my question and I greatly appreciate it!!!



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Hi Joe,
You had said if you would like to figure how much to drop blood glucose to 140, to divide it by sensitivity.
As I wrote before, my sensitivity is now 52 and I did that, divided 140 by 52 and it comes out to 2.6923076923
So if I wish to enter that amount into my pump. do I just enter 2.6? Or being that there is a 9 after the 6, should I increase it to 2.7?
Sorry to bug you with all these questions…

Michelle N

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Hi Michelle @Amethyst8, being conservative, I would enter the 4.6. If that wasn’t sufficient after 4 hours waiting [I do not make corrections closer together than four hours] to get back in range, you are probably ready for another meal and then accept additional correction if, only if, your pump wizzard suggests.
Thank you @joe for your precise and accurate explanation of the correction factor; I had missed what Michelle was actually asking.

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that’s a good question - here’s the rule for rounding

IN this case, if the number following is a 5 or higher… then round up to the next if it’s 4 or less, round down

2.6923076923 would be 2.7

if the answer was 2.642387836572462798547856247652

then I would use 2.6



please understand that if you are uncomfortable making changes you should always check with your doctor I am pretty good at math but I’d hate for you to get sick on account I messed up my math.

Looking at your question again - if you want to go from some number you got on your blood sugar meter… say 250 mg/dl, and then you wanted to be 140 mg/dl the very first thing to do is subtract…

where you are at minus where you want to be = difference

so lets say your bs meter says 250 mg/dl and you want to be 140

250-140= 110 mg/dl

you are looking for a correction (or difference) of 110 mg/dl

so you take the difference and divide by your sensitivity

110/52 = 2.1153846

then round 2.1153846

equals 2.1 units of insulin provided you have no insulin on board (no corrections or meals in 4 hours)

you’re not bugging me at all.

Thank you Joe for all your explanations!!! It really has helped!!!
As you can see, I am bad with math, especially percentages and fractions!
And thank you for your concern over me taking what you have written and using it to do calculations with my pump but I had asked my endocrinologist these same questions and he couldn’t provide an answer!!! He of all people should know.
I never change my pump settings unless he advises me to do so.
But I before I go to exercise, especially using heavy weights, I wait until after I eat to check BG and then drop it down to 140 so I don’t experience low blood sugar while working out.
I’m still wondering how much the number after the decimal point lowers the blood sugar…is it going by 10ths? I’m not sure what to compare it to…I understand 2.5 is 2 and a half. But half of what number? 10? 100? I’m trying to figure how to figure this into my sugar calculations.
The other day, my BG was 343 mg. the bolus wizard suggested 4.3…what is the number 3 being compared to? Three tenths? I’m just trying to understand all these mathematical equations…

Hi Dennis,
Thanks for trying to help me understand and although I don’t know everything under the sun, if you or anyone needs any kind of advice about working out, I’m more than happy to help!!!
I have been working out for many years…:wink:

@Amethyst8 hi Michelle. your bolus wizard is suggesting units of insulin. so in your example 4.3 units or 4 whole units plus (3/10) units of insulin. the pump has a metering system that is “accurate” to either tenths of a unit… 0.1, 0.2, 0.3 up to 0.9 or 9 tenths.

some pumps are “accurate” to hundredths of a unit or 1/100 of a unit. so the pump can deliver 5.15 units, (5 units plus 15/100 units) if necessary. typically hundredths are not used for bolus, it’s used when the pump calculates and delivers basal.

0.1 or 1/10 or one tenth of a unit, based on your sensitivity of 52, will drop your blood sugar 5.2 mg/dl in 4 hours. 0.2 will drop your blood sugar 10.4 mg/dl but since your bs meter doesn’t read in tenths, we’d say 5 mg/dl and 10 mg/dl

don’t get hung up on the decimal. I survived decades with a syringe that was accurate to 1 unit and it wasn’t the end of the world.

Thanks for explaining this to me!!! So 4.3 units is (4 + 3 tenths) units of insulin.
It seems as if the numbers after the decimal point are being multiplied by 5, if I am correct? Like 0.2 will drop BG 10.4.
I know, I used the syringe for 25 years before going on the pump and it doesn’t let you take “half doses.”
Thank you again for your time and helping me with my questions!!!


Thank you for this discussion! My son is 13 and incredibly resistant to insulin. It takes him forever to come down when he’s high and often times meals take up to four hours before he has leveled off. I have never thought about trying to figure this out. We see the endo tomorrow and I’ll be asking about this!

Hi breebrowen,
I experience the same thing when my sugars are high, they take four hours or more to come down and very frustrating, so I understand where you’re coming from!!!
Wishing you & your son the best!!!

Hey Joe,
Are you multiplying the number after the decimal by 5?
I know you are saying not to get hung up on the decimal, but it is important for me to understand how to calculate what my blood sugar will be dropped to if the pump suggests for example, 3.7
Is the number after the decimal multiplied by 5?
I know that 3 units will drop BG 150 mg. But what will the .7 drop it included with the 3? Regardless of the fact that my sensitivity is 52, I know that 1 unit of insulin drops my blood glucose 50 mg.
I really should have gone back to school for math, especially algebra!!!

It’s your sensitivity (52) times the decimal units. If you grab a calculator it’s 0.7 times 52= 37.4. Because it’s less than one ithe answer will be less than 52.

0.7 units will drop your blood sugar by 37.4 mg/dL in 4 hours

Your sense is correct about 5. The 5 comes from 52. 52 times 0.1 is 5.2. For each tenth unit of insulin tour blood sugar drops about 5 mg/dl

Oh ok, I understand now. Thanks again for helping me understand!!!