Any advice on how to make the G6 more accurate and reliable?

We just switched over to the G6 from the G5 with the tandem t slim X2 and basal IQ. We are on the second sensor because the first one was so far off much of the time. We tried calibrating the first one three times 15 minutes apart - Dexcoms advice. It would be reliable for a while and then be four to six mmols off for a while then drift closer to accurate again. The wonky readings already missed a middle of the night low of 2.6 because it was jumping all over. As a result basal IQ kicked in then resumed delivery when it should not have. I can’t imagine dealing with this kind of inaccurate unreliable data when control IQ comes along in Canada. The second sensor we decided to not calibrate for the first 48 hours to see if that made a difference. It was still at least 4 mmols off at times. Does anyone have any tips on how to make the G6 more accurate eg. Calibrating once a day, not putting in the code, any ideas at all are appreciated. I was so excited about the basal and control IQ, but if it’s only as good as the numbers it relies on, I will be very disappointed if things don’t improve. She is well hydrated and we have tried back of the arm and just above her waist on her back. We’re not new to Dexcom having had the G4 and G5 but frankly I’ve seen a lot better accuracy are those models than we’re seeing now.

If you aren’t presoaking, there’s no purpose at all to calibrating in the first 12 or 24 hours.

Mine do very well with a 12 hour presoak and no calibration (yes, I do cross-check using fingersticks, just don’t bother doing putting in the number as a calibration).

I have lots of belly fat and some here not so blessed may have more G6 issues it seems.


Okay, we’ll try the presoak. She’s not super lean either, so the site’s she chooses should be okay - at least they always have been with G5 and G4. Thanks.

Oooh, ouch, yeah those are bummer readings.

You can try not entering the code for automatic calibration and just calibrating with manual finger stick. That’s what I would recommend upfront just because of your level of inaccuracy. Sometimes we see runs of inaccurate sensors in a shipment. This isn’t permanent, but it sure might feel like it - depending on how many bad sensors you see in a row. Be sure to call Dex for replacements once you see 3 bad ones in a row. Three is the maximum that they will replace at one time.

Be sure to let me know if you think running ‘no code’ helps with accuracy. I think it helps me, but I would like input from others since I tend to make this recommendation. Thanks a bunch.

My experience has been that when I see that level of poor sensor performance, it doesn’t recover to an adequate degree and its best just to pull the sensor and replace it. Call and report to Dexcom for sure.


The G6 is amazing when it’s working, but sometimes you get a terrible sensor. What a bummer that your first one or two is off. Just let Dexcom replace the bad ones. It might be your whole box. FYI, you can call Tandem instead for replacements, they’ve got better customer service.

Personally, I calibrate immediately after the first data point with the G6. They nearly always fall right in line after that. But then again, I’m fortunate enough to be the optimal body chemistry and don’t have to pre-soak, so that might not work as well for you guys.


Okay, we will try that too. Calibrate right away…after a good presoak.
Thank you.

A brand new sensor I calibrate immediately and then wait about 2-6 hours to do another calibration. Sometimes the next morning I will do one more calibration to fine tune it as I like them within 5 points.


Okay good. I’m glad people calibrate right at the beginning because there are a lot of people who are of the mind that you just leave it to straighten itself out over the first two days. I don’t like that method because frankly two days of unreliable readings it’s far too much to accept, especially when dosing with the X2. I am going to try getting it straightened out right from the start on the next one. Thank you

Let us know if that works. Cali may or may not help 70 points off, but lets us know and we will investigate/brainstorm further because that is such a bummer.

Yes. I will report back. Thank you to everyone for your suggestions.

What usually happens with a new sensor for me is it’s way off when it first starts, I try to make sure I am about a 100 so I don’t go out of TIR lol…But it has been known to try to come on at 180 or 50 so I am ready for an immediate calibration. Then it will still be off which is still annoying so depending on how far off it stays depends on how soon I do the next calibration. That second one usually after a couple of hours makes it fall in line. By the next morning it might still be off enough that I fine tune it.

But if they stay too wacked I have been known to put in several calibrations and you can then get a message to calibrate again to retain the first calibration, this can start a loop of it wanting more calibrations. When it won’t stop asking I am willing to just stop and restart it. This only happens if you try to calibrate it too much in a short period of time.

I just expect the first 8-12 hours to be out of range. I just let the inaccuracy ride until that point and then if needed calibrate.

I lived without CGM for 30+ years, so 12 hours isn’t an issue.

I agree with you on this. I use another automated insulin dosing system, so I fully appreciate what a wildly inaccurate CGM means with automated insulin delivery. With the Tandem pump, can you switch to “open loop” when you know the CGM data is bad? Does the X2 pump allow you to turn off the Basal-IQ and just run in manual mode? If it does, that might be a temporary solution for you.

Your topic caught my eye since I will be switching to the G6 when the Dexcom G4 server goes dark at the end of next month (June 2020). I’ve read many reports like yours and that causes me concern. But I also know that a very large slice of G6 users are happy with their CGM.

Are both of your first two sensors from the same manufacturing lot? If so, do you have any sensors you might try from a different lot? I imagine that some sensor lots can be bad and get by the quality control process. Just a thought.

Good luck and please keep posting. I’ve got two more G4 sensors to use then I’ll finally be joining the G6 era.

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Hi Terry,
Yes that’s a good idea to turn off basal IQ when we know the numbers are wacky. I have to report the numbers have now been quite accurate since the calibration on day 2. We keep checking a few times per day and it’s pretty spot-on. We haven’t calibrated since then and she’s on about day five. We don’t have another lot since this is our starter pack we’re using. I will keep checking throughout the 10 days but I’ve definitely got some good tips here about soaking and calibrating early in the first day or so.
Dexcom advertised finger stick free which sounds fabulous but I’m not sure we’re ready to put that kind of trust in a system that hasn’t proven itself to us yet. we have decided that if it isn’t really really accurate and dependable we will not upgrade to control IQ because it’s one thing to suspend basal on inaccurate numbers but it is entirely another thing to dose corrections based on inaccurate numbers. That’s just downright scary.

Also make sure you are hydrated. G6 works much better if you are properly hydrated.

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Yes hydration is never a problem. DD drinks a pile of water - guess you can’t really pile water but it’s a lot😂

I know they advertise no calibrations needed. And I’m pretty sure they sold Medicare on the fact you don’t need to calibrate so they don’t have to supply a meter or test strips anymore.

But all through their manual it says when in doubt calibrate. AND when you call or submit the form they want to know what numbers the sensor if off by and want it off by at least a certain amount. How could you give then that information unless you checked it?

Personally them pushing the no need to finger stick and the numbers I’ve seen mine be off for in the first 12 hours if I don’t calibrate is fairly scary. Unless of course you go by the fact that they once told me I should give my sensor 3 days to be accurate, but then it’s not really a 10 day sensor either.

So yes, I calibrate and I love a restarted sensor over a new one.


I typically do not calibrate the G6 unless on the first day of the sensor it is way off (more than 20%). However, for the first time since using the G6 in > 1 year, the Dexcom app on my iPhone displayed a notification to perform a calibration. This has occurred 3 times already in the past day. The finger stick was not off by much though, < 10%.

I think calibration notification occurred due to an extreme high BG of 300 at completion of the warmup period at midnight. I didn’t realize it as I was sleeping, but calibrated at 3 AM upon waking; finger stick showed 260! It turned out I had a bad pod and was not getting any insulin for 5+ hours.

I have a Tandem t slim X2, also. I started using basal IQ in the fall of 2019 along with Dexcom G6. I liked it very much. Then the opportunity to upgrade software to Control IQ came along and I did that in Feb 2020. It is working well for me. However, when I first started using Dexcom G6, I had some poor correlations between CGM and fingerstick BG. The first time this happened, I calibrated numerous times, and the problem got worse. Tandem sent me a replacement sensor. I spoke to my diabetic educator and she said that I SHOULD NOT BE CALIBRATING if using sensor code with G6. I never have calibrated again and my correlation is acceptable even during the first 24 hours with a new sensor. I have found that after years of inserting my sensor on my abdomen, I seem to have better correlation with placing the sensor on my upper arm. I also use a Dexcom overpatch - this keeps the adhesive in place. Supposedly it does not prolong the life of the sensor, but it does seem to keep everything in place and possibly decrease the water that may get around or under the device. I assume you get CGM readings on your Tandem pump. Correct me if I am wrong. Anyway I also read that there is better correlation if the pump is kept closer to the side of your body where the Dexcom sensor is placed and it is best to have the top of the pump facing away from the body. These may seem like little things, but together they have worked well for me. I hope this helps. Keep in touch. Jane

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Except that contradicts Dexcom’s own instructions/user manual. They clearly cite several examples of when you SHOULD calibrate.
Sometimes the G6 even asks for calibrations, even when started with a code Unfortunatelyy, the DE certification doesn’t garauntee complete knowledge in all things diabetic, and definitely not in this case if they’re speaking in such definitive (“never”) terms…

Since we’re all made differently, and these technologies seem to interact differently with all of us… Find what works for YOU, and stick with that.

Personally, I’m going to keep calibrating immediately and whenever else necessary because I won’t tolerate a misbehaving sensor when my automated dosing depends on it’s accuracy.