How do you determine your insulin to carb ratio?

I’ve had diabetes since I was 12, I am 25 now. I was under the impression that all diabetics have a 1 unit : 15g carb ratio. Only now am I reading here everyone is different and that ratio changes.

I am assuming I need to see my endo for this? I live in Guyana and make yearly trips to Canada for all my appointments.

I am also guilty of not keeping a journal of my blood sugar levels for years, I sort of just test and adjust as I go along. Very irresponsible, I know, but at the very least I managed to keep my AICs around 7.5%. If I need my endo to change my carb:insulin ratio, I’ll be in trouble, as I don’t have any records.

I have 3 weeks til my appointment, I guess I should start some detailed records from now.


Your endo or, in many cases, a “diabetes educator” can help you to determine what your carb ratio might be, but in the end the bulk of the work … i.e. the record keeping … is going to fall on you. I’m never sure how many of “us” determine and change such things with perhaps only an aside to the endo to let her/him know we’ve changed something.

That certainly is pretty much how I’ve done things for so long now that I couldn’t really tell you how long it’s been.

The first step in figuring out what your carb ratio might be is to make sure that both your basal rate(s) and duration of insulin activity (DIA) are correct. If those are out of wack then whatever results you get for a carb ratio will be skewed and not accurate. You can come up with a number which will pretty much work in the context of your other (incorrect) numbers, but if you ever change your routine it can turn around and bite you on the a$$.

What tools are you using to manage your D? I am assuming you are using MDI, yes? How often can you test your BG (Blood Glucose) during a day?

Do you use a so-called “smart phone”? There are now “apps” which you can use to log your information. I tend to rely on my pump to track my information for me. But if I didn’t have that I would probably feel more comfortable using an app of one kind or another as that just tends to end up being more organized and easier for me to read than if I were to use paper.

a lot of people here use mySugr - it’s kind of a fun app too

my I:C is 1:9 in the mornings and 1:15 the rest of the day

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@Luffy, there are some “rules of thumb” that employ a calculation to figure your approximate insulin to carb ratio or I:C. John Walsh uses the 450 rule. You may read more at his diabetesnet site. He calculates the insulin to carb ratio, he calls it the carb factor or CarbF. It’s the same thing.

I:C or CarbF = 450/total daily dose of insulin

For example, if you use 40 units a day then, 450/40 = 11.25. Or you could round it out to 1:11.

Having said that, when I plug in my total daily dose of 32 into the formula I get, 450/32 = 14. That’s a 1:14 ratio. I actually use 1:4 for breakfast and 1:7 for dinner. So, I would recommend using this, or any other formula simply as a starting point to do your own personal experiments.

If I were you and wanted my doctor to weigh in with his recommendation, I would just keep a two week record of all insulin delivered, both basal and bolus, blood glucose data (the more the better), and a food diary that includes at least a carb count for everything that you eat during that time. I would also record all exercise duration and intensity as well as the time of day of that exercise. 14 days is more than enough data to give the doc what s/he needs.

Better yet, doing a 14-day record keeping session would give you a better idea how your body works. What you learn can have an effect on your blood sugar control all day every day. You only see the doctor a few times per year and the overall effect s/he has on your health is small. The best investment you can make is the one you make in your knowledge!


I am a fan of self experimentation. For those who have virtually no natural insulin production, a proper match of insulin for a meal brings your blood sugar back to the starting point at 3-5 hours. So the best thing to do is perform human experiments. Take a “fixed” amount of carbs (preferably simply carbs such as dextrose) and bolus and see what happens. If you are still high at 3-5 hours then you didn’t bolus enough. If you go low, then you overbolused. Adjust your bolus and repeat the experiment (I recommend modest changes like 10% at most). Eventually you will figure out your ICR. Most people have different ICRs based on what time of day and unfortunately for most people the ICR varies depending on “context.” If I sleep poorly, overate carbs the day before, am stressed or simply have “stuff” I may require different amounts of insulin.

I also find that I respond differently to simple carbs versus complex carbs and wheat based carbs are worse than other carbs. Your Diabetes May Vary (YDMV).


i admit that i have not read John Walsh’s book, but i was interested in how you (he) found this formula. i have for the most part been on a 1:10 ICR most of my pumping life. but i only use a daily total of 20 units per day. if i divide 450/20, i end up w/ 22+ . does that mean my ICR is 1:22???
totally confused.please help.

btw, i forgot to mention that i am not insulin sensitive but the opposite. and i always thought that b/c i am so little, i would require less insulin than my other, more plump, D friends. obviously, this is not the case.

Trial / error and taking notes. If you’re consistently getting spikes at 1:15, try 1:14 for a while, then 1:13… So on until you find a point of equilibrium… Of course it’s not a perfect science and you’re not going to hit the bullseye every time but if you’re generally spiking more often than not, you should adjust your ratio just as if you’re dropping more often than not you should also adjust…

Wow this isn’t even in the right hemisphere for me… I am not a big fan of magic formulas like this… They don’t seem to even get me anywhere near my ballpark

I’m not here to defend John Walsh. I stated my divergent experience with his formula. I agree with you Sam that personal experimentation is usually the best guide. As I’ve written before, even if a formula gets you close, it will never be perfectly consistent. We each need to respond to the dynamics inherent in blood glucose metabolism.

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If you follow the link I provided above you may read about John Walsh’s work. I wrote above how my experience is much different than his formula. If you accepted his formula as a starting point,however, and then experimented and made adjustments, then you might find what works for you. In any case, I think any formula, even one that’s worked before, should always be looked at with some skepticism. Diabetes is not a static disease. It changes every day, just as we do.

They’re just based on a lot of assumptions, if I was following the ada diet and eating 250g of carbs each day it might get me somewhere in the ballpark… I guess with no further information for a baseline they have to start somewhere…

There’s also the wild card of how much natural insulin any person still produces. If you’re producing 30% of what’s needed then that’s a significant reduction of external insulin needed.

Terry, i cannot find the link you recommended in your response. however, i am buying John Walsh’s book this afternoon.

i am still confused. as to this formula, i use approximately 20 units per day. by following this formula, i would divide 450 by 20, but that ends up being 1:22 ICR. thats a crazy ratio. currently (and for all my pumping life), my ICR has been approximately 1:10.

am buying Walsh’s book this afternoon. but can you explain this to me? i am completely confused.

by the way, i forgot to include: my total basal rates for the day are only 10.4 then i add in the carbs i account for and then i get a total daily insulin use which brings me up to a total of 20 units.

Daisy Mae

Here’s another link:

Walsh’s books are very good and packed with good info, but I wouldn’t take this or any other dosing formula too seriously. You have to know what works for you… Which no formula will ever dictate, your years of experience and close observation and note-taking will.

the formula that i am on has worked for me ever since i have been on the pump. 1:10 ratio. but i did order the book from Barnes & Nobel and plan to read it cover to cover anyway. i’m certain that i can still learn a lot from what Walsh has to say. I am also going to order that Ponder book on line (as it is not sold in stores as far as i have been told).

The ponder book just arrived at my house I’m looking forward to reading it.