I really suck at this, could use some tips

The Tandem t:slim pump setting which determines how much insulin is delivered for a given amount of carbohydrate in a meal is “Carb Ratio”. If abbreviated it would be CR not CF. The Carb Ratio is also referred to as the I:C ratio or the Insulin:carbohydrate ratio.

The CF or Correction Factor determines how much your BG falls for 1 unit of insulin. This settings determines how much insulin to deliver to reduce a high BG to your target BG setting.

Insulin delivered to cover carbohydrates in a meal is called a meal bolus. The amount of insulin for a food bolus is determined by your Carb Ratio. Insulin delivered to lower a high BG is typically referred to as a correction bolus. The size of a correction bolus is determined by your Correction Factor setting.

What advice has your medical team given you for determining your pump settings?

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Really great summary of the basics in your post, and we’ve seen at least one post recently where it seemed like a relatively new T1 (a year after dx) was put on a pump and told almost nothing about these terms and concepts. I’m wondering if there’s a trend developing with these AID pumps where they think the pump is going to do everything for you so you (and they) don’t need to know anything, just turn it on and let it do the rest. Sure would be a lot easier if that were true. It’s not.

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I’ve had some trouble getting in touch with my endo, but I have an appointment on Friday. Hopefully that will help some. I haven’t spoken with him since I started with the CGM, but yeah, I wasn’t aware of some of how it worked. I’ve tried to ask questions and learn more about it, but a lot of it is still relatively new to me. Part of the issue si that there’s been several balls in the air at the same time. I’ve got how many carbs I’m eating, what my meal correction is, what my CF is, what my basal is, whether or not the injection site is properly working, and all of that can affect what my numbers look like and trying to adjust them all at once is a bit overwhelming at times. But, one small step at a time I guess!

Diabetes is 24/7, doctor assistance happens much less often. The solution? You need to steadily build a foundation of knowledge that will make needed consultation with your doctor a rarity.

We still need doctors but for moment to moment assistance you’re much better off depending on yourself. This competence cannot happen overnight but I would recommend the books that @Sally7 listed above plus Dr. Bernstein’s Diabetes Solution and Adam Brown’s Bright Spots and Landmines.

Your personal diabetes knowledge is the human software that runs your glucose metabolism on manual. This is no small task! Invest in yourself and chip away at the list of many fine books on this topic. It will take time but if you prioritize it, after five years you will be the metabolic expert on you. No doctor will ever know your glucose metabolism that well.


Well, I ordered all those books! I’ll be reading them when they arrive! Thank you.

I’ve heard from other people who have had T1 for years and only recently got a CGM, whose initial response was along the lines of “OMG, I had no idea this was going on!” When you go from finger sticks 5x/day or so, little snapshots, and then suddenly see the whole movie it can be quite gobsmacking. Suddenly you see what was going on “in the dark” between finger sticks, and it’s like turning the lights on in your kitchen at 3am and seeing cockroaches scrabbling for the corners. I’ve coined the term “CGM Shock” for it. And then it’s “What do I DO about this!?!”

Pre-bolusing is one thing. Always surprised that Dr’s prescribing CGMs for people don’t seem to know about that. Probably its single most useful application for most of us. Another is, yeah, some of the newer oral meds developed for T2 that can actually be very beneficial for T1. I haven’t tried Victosa, but I can emphatically endorse Jardiance for flattening out your curves. My endo started me on it about 2yrs ago, and it has been spectacular. I credit it with getting me to a sub-6 AIC for the first time since I was dx’d in 1983. It’s off-label for T1 but I think most endos are willing to try patients out on it on a case-by-case basis. Worth asking.

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Remember that if you have turned the pump’s C-IQ feature on, then the pump is attempting to deliver additional insulin by increasing your basal rate when you BG is above your target BG setting. This is also a piece of the puzzle to consider.

Did you get any pump and/or CGM training from your endo’s staff? How about pump training from Tandem? Your endo’s staff should have placed you in contact with a trainer from Tandem.

Have you been uploading your pump’s data to Tandem’s t:connect database? When you do that, you can also sign in to Tandem’s t:connect database portal to review the data uploaded from your pump about CGM results and insulin bolus & basal delivery.

I’ve had a little bit of pump training on how to work everything. I’m all signed up in the Tandem database. I’ve talked with the trainer a little bit, but she’s helped me with some of the basic things. Haven’t gone over much into how to correct my insulin settings, other than to say that the doctor typically is the one to do that and she couldn’t make any recommendations. I’ll get some of these books read and figure out how to better fine tune it myself if I have to, and then the doc can help when he’s able, I guess.

For whatever it’s worth, the Tandem trainer I was in touch with wanted me to review the ebook (PDF) at the link below before doing a training session. It looks like a (possibly too simple) overview of pump training. But maybe it might help put some things into context for you.

Guide to Successful Pumping (Tandem’s pump workbook)


Please talk in depth to your endocrinologist. He will need your blood glucose values from at least the last 2 weeks. Upload on T :Connect if possible. You can print the log book and other reports for your doctor to review. There are formulas that your doctor should know in order to set your insulin to carb ratios and correction factors, and basal rates. These settings may vary from meal to meal and time of day. I have 6 different settings in my profile. I need more insulin at breakfast than dinner for example. My basal rate varies throughout the day. I hope this helps. Jane Gwinn


You have gotten so excellent tips from a number of regular contributors here. I’d like to toss out a few minor, additional thoughts:

  1. Does your endo work with one or more CDEs (Certified Diabetes Educator)? And would your insurance cover appointments with a CDE? A good CDE often has more time to spend with you and often has more hands on experience with a pump and CGM than an endo. If you can find a CDE that is either T1D themselves or has a kid/spouse/sibling that is, you can often learn a lot because they understand the 24x7 nature. While you might think that would be hard to find out, your endo will know …

  2. Setting basal rates, IC ratios, and correction factors is tricky … both because all those values probably vary over 24 hours and because even if you try to run the same experiment 10 different times, at some level you are going to see 10 different results. I was lucky in that I began using a pump 1-2 years before Basal-IQ and then Comtrol-IQ became available. That forced me to try to determine basal rates, IC ratios and correction factors at different times of the day. For me, at least, my basal rates are lowest at night and my IC ratio is the highest then. If I used those values around the clock, I would definitely see big postprandial spikes. Everyone is different, but I think that an argument can be made for turning OFF Control IQ from time to time to check your settings a different times of the day. I think that it was @DrBB who commented that this first generation of closed loop isn’t yet good enough to just let it run. While I expect that we will all see more capable closed loop systems over the coming years, we are still at a point where our settings DO play a significant role.

  3. Finally, meals with lots of simple carbs are hard to make spike-free … at least I can’t avoid that. With CGM, in particular, it makes it easier to also test food and dietary choices. Maybe something with lower total carbs, more complex carbs, or even more fat can more easily flatten a peak than a big slug of insulin.

Best of luck. You are working with some pretty amazing tools … but it does take time and effort to master them. (Actually, I’ve never “mastered” anything associated with T1D … but I am still getting better at using the tools that I have at my disposal.)

Stay safe!


I believe this illustrates the single most important point to implementing effective ongoing treatment. Diabetes doesn’t stand still, neither should we. If you can learn how to detect when changes are needed and how to do the personal experiments that will inform your tactics, that is the key.


How did things go at your appointment with your endocrinologist? Jane

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I’m fairly new to a pump (Tandem t:slim. I am not on CIQ); have used DexCom cgm for 10+ years. My CDE did all my pump training. I tracked carbs, insulin dosages and post meal BG for weeks prior to starting on the pump. No training on how to adjust I:C, correction factor or basal. I am very sensitive to insulin–CDE had me change 4 of my basal rates in one day and I got a lot of fast BG drops and alarms. Prior to being on a pump, a different CDE had me change one factor, maintain that for a few days, then change again if needed—seems being on a pump requires the same for me. How do you know if the I:C ratio should be changed vs the correction factor? Someone mentioned watching BG readings after a meal—how long after a meal? I’ve been T1D for over 60 years and am looking for ideas on how to level things out without so many fast BG drops and help me to be in range more. (I do count carbs carefully, too) Thanks!

Have you looked at the Tandem online ebook linked below? The book’s second chapter, Customizing Your Insulin Dose Setting, covers the settings you seem to be asking about. Perhaps it might help? (The chapter goes over some of the arithmetic I wave my hands at below.)

A Guide to Successful Pumping

The approach I take to decide which setting to change is to test them separately.

The Correction Factor (CF) is only about correction boluses. It controls how much insulin to deliver to lower your BG by a given amount. Carbs should not be a factor when testing your CF settings.

To sanity check your Correction Factor, enter a correction bolus into your pump when your BG is at a stable elevated level and you haven’t eaten anything.

As the bolus takes effect you should see you BG drop back to your target BG setting. If your BG is not lowered enough, then your CF may be too high. The Correction Factor is just the amount your BG should drop for 1 unit of insulin. So if the CF is too large then the pump assumes less insulin is needed to lower your BG.

Similarly, if the Correction Factor is too low, then your BG will be lowered too much. You may need to consider increasing your CF.

The I:C ratio is about food boluses, not corrections. It specifies how many grams of carb one unit of insulin will cover.

To see how well your I:C ratio setting is working, wait until your Blood Glucose (BG) is steady at approximately your target BG. Then bolus for and eat a known amount of carb.

Your BG should go up, peak, and then come back down to your target BG. If your BG doesn’t return to your target BG but instead stays high, then your I:C may be too high. That is, the I:C setting indicates that 1 unit of insulin will cover more grams of carb than it actually does. So you may want to lower your I:C ratio slightly.

If instead your BG falls below your target BG, then your I:C ratio may be too low. That is, 1 unit of insulin will actually cover more grams of carb than your I:C settings says it will. You would want to think about raising your I:C level.


I find that the lead time to do a meal bolus before a meal varies hugely with the type of insulin I am using at the moment (I switch between them a lot). For me, the numbers are:

  • Novolog, 20 minutes
  • Humalog, 10 minutes
  • Fiasp, first 5 minutes of the meal
  • Lyumjev, as I finish the meal
    And what I’m eating determines whether I use an extended bolus or not. For example, for Fettucini Alfredo, I go 50 now, 50 over an hour. For ice cream, it would be all at once.

Another rule I use us that I make very small changed in my basal, carb ratio, or correction ratio at a time, and only change one of those st a time.

I also have six time slots on my t:slim: midnight, 4 AM, 7 AM, 4 PM, 8 PM, and 10 PM. That has worked well for me over the past 6-7 years.

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Thank you! I will check into that book. I appreciate your response!

I’m using Novolog in my pump. I do pre-bolus and have my timing down for that. I think I have gastroparesis (minor case, apparently)–for me a bolus for my evening meal is the tricky once. Dietitian said I have to experiment to find out what works for me. And yes, what I eat is also a factor for that time of day. I have multiple basals set in my pump and totally agree with you on small changes and only one at a time.

Thanks for your comments!

Sounds like there is a lot of good advice posted here for you Jakewriter1. As someone said it may take a little time to acquire knowledge and experience in fine tuning your pump. I think it was also John_S2 touched on it - managing your carb intake or just as important the type of carbs you are ingesting. I think it was also mentioned about consulting a diabetic dietician to learn as much as possible about carb intake, type and how things like protein and fat affect your BG.

All in all sounds like you are doing the right things and I have no doubt you will get there! I admire that you are inquisitive about finding answers and when you do coupled with your own findings from personal experiences you will be all the better for it!

Best to you, -Steve

This is a perfect example of how each of us is so very different in our treatment plan. There are many here that spend a lot of time fine tuning, detail oriented and driven to be the best. And than there are some who want easy and user friendly.

While I strive for my personal goals, I don’t let those goals control my life. After all these years, I want easy. I want to not have to think about everything, all day long. So for me, I use whatever insulin my insurance company is covering this year. I have two profiles, off day and work day. And each of those profiles has two different basal rates. And for daytime and one for overnight. I do have different carb ratios for meals but otherwise, pretty easy and straightforward. I have come a long way from the 8 different basal rates during a 24 hour span. Took me a long while to realize that with a 2 hour lead time for the change to happen, less was better for me.

And with my TandemIQ, I have the easy I have been hoping for! I love being able to not worry about what not eating for most of the day will do to me. The little pump just does its thing and I go on with my life. Or if I am really working hard during my walks, my little pump just does its thing! I so love easy!

And in a few weeks, I start back up with the clinical trial with the iLet pump. Not sure if I will be assigned the control group side or the tes side, but I have been told if control side, I will get the new pump for the second three months. So either way, I will still get to try it for a longer span of time, instead of just the 6 days last time. And I am hoping this will take another thing for me to think about off my plate. No more counting carbs!!! Heaven!

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