Dexcom G6 Calibration question

So I restarted a really well-behaved sensor and it’s been really off now. It started out (after restart) about 100 units over my actual BG, and of course I couldn’t help myself from “rage” calibrating…:wink:

Anyway, now I don’t know how many times I’ve calibrated it, but it still is about 70 units high. Any suggestions? I know I goofed up and should have just left it alone, but…

What should I do now? Is it salvageable? Or should I just put on a new one?
(I restarted it with the code.)


As I mentioned on the other thread about this, I don’t think code AND calibrations is a good idea.

Entering the code is one way the sensor can be calibrated. Entering BG numbers every 24 hours is another.

But when you do both, the two methods can interfere with each other.

Since you mentioned that you restarted it, how old is the sensor? If it is over 10 days old, it might be a good idea to just scrap it and start with a new one.

Just my general observations based on experience and a lot of reading and discussions with Dexcom - if entering a sensor code and not calibrating works well for you, great. Do that and go with it.

But if you find that entering a code does not work well for you, then try skipping the code and just do calibrations instead.

But don’t do both.



I use code for initial session. If i restart, i use no code and calibrate. Often requires more calibrations in first 4-6 hours to get accurate.


I used one of my son’s sensors and an almost dead transmitter (I’m a non-diabetic, he’s a T1) just to better understand and give my son some extra spirit. Also, I’m a geek when it comes to technology, and I just wanted to collect some data.
Anyway, I restarted the sensor and it went high immediately. I did one correction after an hour, but held off doing another one. After two hours it settled in and was fine. I used the code to restart it. I agree with the others, from our 1.5 yrs of Dexcom G6, if we have to correct more than twice in a few hours, the sensor is generally on its way out.


@Eric @MM2 @Andre

What are the best practices for no-code and calibration?
Range to calibrate in?
Number of calibrations per day?
Timing? How far apart?
I’ve never done no-code before and am a little unsure about it.
Thanks! :blush:

P.S. I’m going to end this sensor and put on a new one. It’s 11 days old, and has been 70 to 100 units above my BG ever since I restarted it.


The system automatically prompts for calibrations in 12 hour intervals but does not take into account whether your BG is level, rising, or falling. I prefer to calibrate when my BG is level but sometimes when there is a huge difference between CGM and meter reading I will calibrate anyway out of sheer frustration with the system.


I think it is best to calibrate when your BG is relatively flat. I think that is 100% agreed on by Dex users!

I have also heard people say to only calibrate when you are in range, but I don’t think that is absolutely necessary. If you calibrate when you are high, then your sensor knows what high looks like. :man_shrugging: Same for calibrating when low.

That :arrow_up: goes against the common belief of many Dex users. But to me, calibrating when flat is more important than calibrating when in range.

So this is what I do:

  1. I calibrate when the receiver or app tells me it is time to calibrate, but only if flat.

  2. I calibrate whenever it is significantly off, but generally I will only do it once. Like if I have recently calibrated, I will give it a chance to get its act together before calibrating again.

  3. When it is a more urgent situation, like the Dex number is way off and I am going to bed and I want it to be correct, then I will break rule #2 and double calibrate. I enter the calibration number twice back-to-back. That brings the Dex immediately in line with my actual BG number. Again, this is only when I am unable to wait, like bedtime.

  4. I try to avoid excessive calibrations. As mentioned above, I only do it when it is either way off, or it tells me it’s time. I don’t do a bunch of extra calibrations.


Thanks so much! Those are all great instructions. :+1:
I feel more confident trying the no-code option.


What if you start a new sensor and it is immediately way higher than your BG from finger sticks?
How soon do you calibrate?


Is that one you entered a code for, or a non-code sensor that you are calibrating?

On the first time you calibrate the sensor, it should immediately take the value you enter when you do the initial calibration. 2 hours after the sensor start, if you enter 100, the Dex should go right to 100.

For any subsequent calibrations later on in the sensor life, it will generally go halfway. Like if your sensor says 120, and you calibrate 100, it will go to about 110.

So I am trying to understand your scenario. Are you saying after you did the initial calibration it started to go wacky?


I restarted a sensor on day 10 with the code, and it immediately was 70 units higher than my finger stick. And it kept going up.

But, I’m asking what to do if that happens with a new sensor, code or no- code.


The first 24 hours are generally not great with a new sensor. But when you calibrate it two hours after the start (the initial calibration), it will at least start off at the right number.

If it shows bad numbers soon after the start, that’s kind of the nature of new sensors. I’d say generally try to wait 12 hours, because that’s when it will tell you to calibrate.

But if it’s off by more than 20%, calibrating it sooner is okay. That’s kind of Dexcom’s advice. They say 20% when over 120, or 20 points when under 120.

So for example, if your BG is 80 and the sensor says 100, that’s within 20 points and it’s under 120, so leave it alone.

But if your BG is 180 and the sensor says 230, that’s more than 20% off and it’s over 120 so calibrate it.


What’s the best way to restart? I had it work out once but fail a different time. Approach was to end the session, disrupt the connection between sensor/transmitter for 30 minutes then try to start a new session.

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@Eric @CatLady

So if you are using the no-code option, what time during the day do you put on a new sensor?

I assume the first calibration is asked for right after the 2 hour warm-up?

And then another calibration asked for 12 h later? Are all the calibrations 12 h apart? Do you have to do them then? What happens if you don’t?

So, you have to do some planning as to when you put on a new sensor?

(Sorry for all the questions)

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I put it on after a shower, which is generally in the evening.

I will try to do it so that it will not give me a calibration at a lousy time. Like don’t do it right before you go to sleep. Do it at least 2 hours before!

  • The first time it will ask you to calibrate at 2 hours (after sensor warm-up).
  • The next (second) calibration is 12 hours later.
  • The next (third) calibration is 12 hours later.
  • Every other calibration after that is 24 hours later.

So depending on when you wake up and go to bed, pick a time that makes sense.

Like for me, if I start the sensor at 8pm, that works out well. First calibration is at 10pm. The next one is at 10am. The next one is at 10pm. And then it is 10pm for the rest of the sensor.

But suppose you picked a lousy time? No big deal. Like if you are supposed to calibrate it at 5am, you don’t really have to! You can wait until you wake up. No big deal. It will still give you your numbers even if you don’t calibrate it! So you can always adjust it by calibrating it later, or earlier. No bid deal at all. Doing that won’t mess anything up!


Thank you!
You are amazingly patient and nice for tolerating all my questions!

I’m one of those people who have to have every detail planned out, and wants to know exactly what to expect (as much as possible :wink:).

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I always have a plan but rarely follow it. :joy:


I have also had experiences with my sensor being way off after insertion. I have always used the code. I also use the xDrip application for additional information. I have noticed that the G6 transmitter in some cases rejects the calibration with errors like 6 or 16. The xDrip Log report always displays any such messages from the G6 transmitter. For most of my cases when I do have a calibration problem it only lasts for a short time after a sensor insertion. If a calibration of more than 20% is attempted I usually get a rejection message from the transmitter.
I use both my smart device with xDrip and also the Dexcom receiver. The receiver does not show any calibration error messages when I use that device, just no calibration adjustment.
I now never attempt to make an adjustment more than 20% at a time making several calibrations.