New To Dexcom G5; How Often Do You Need To Callibrate?

just started on my dexcom G5. for the most part its been very accurate, but i find that several times during the day its reading is really off.

i was just wondering how frequently others experience this problem, and how frequently you will recallibrate your receiver.

please chime in about your experiences. i would like to know if i have actually found my sweet spot on my body where i get the best accuracy. i tried it on my arm, and on my thigh and i had terrible accuracy problems. basically, there was no accuracy. but now i am wearing it on my upper left buttock beneath my hip, and it has, for the most part been pretty close to my finger sticks (maybe +/- 10 points or spot on) however, i have experienced really wacky readings for which i have had to recallibrate it.

what is “normal” or at best, “acceptable?”

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The important thing is to see if the Dexcom will eventually “catch-up” with your BG. It can be far off anytime your BG is changing rapidly.

But once your BG becomes flat, does the Dex finally start to match-up better? Or does it stay far off?

Other than the normal calibration signals it gives you every 12 hours, I would advise that you only calibrate it if your BG is flat and you have given the Dex enough time to catch-up, but it never catches back up.

Like if you are flat for an hour and the Dex is still “far off”, you should calibrate.

“Far off” is anything more than 20% of a difference with your meter when above 80, or 20 points off of your meter when below 80.

For example, if you are flat and your meter says 100, your Dex should be between 80 and 120 (that’s 20%). If it is not - and you have given it enough time to correct itself - you should calibrate.

Another example, if your meter says 70, your Dex should say between 50 and 90 (in this case since you are below 80, you don’t go with percentage, you go with points).

But if your BG is changing, don’t do anything until flat again.

Does all that make sense?


the rest of your answer makes complete sense, but this part i dont understand. can you clarify it for me, please?

Whenever your BG is below 80, you don’t use percent to see if it is close enough, you use points.

Dex should be within 20 PERCENT when you are above 80.

Dex should be within 20 POINTS when you are below 80.

So just do your BG check first, and see if you should be using percent (if your meter is above 80), or points (if your meter is below 80).

Is that better?

All of that aside, only calibrate if you are flat and the Dex hasn’t caught up.

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I used to calibrate twice per day. I find it works better for me to calibrate once per day, except on a new sensor I’ll also calibrate after 12 hours. My bg is flat right before breakfast, around 45 minutes after I get up in the morning, so that’s when I calibrate. And I restart or replace a sensor in the evening. I decided that when I calibrate more often, I just end up chasing errors higher and lower without actually improving the future accuracy of the CGM. That’s why I stick with one really careful calibration per day.


what i am curious about is how often do you need to calibrate. for example, my cgm once read 174 when my finger stick was only 85. obviously this required my calibration. this reading was way out of range. but then i recalibrated my cgm and all went back to normal. so, that being said, my meaning was how often do you need to calibrate?


This should be QUITE the abnormal circumstance. If this happens frequently, there are larger issues then calibration.

Which is possible as I know the cgm did not work well for you in the past.

EDIT: When the cgm read 174 (in your example) was the graph of the cgm a straight and horizontal line? Or was the graph of the cgm showing a rapid increase or decrease?

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I calibrate when it asks for one. I am using G4, but should be similar to G5, since sensor is the same.

If meter BG is way off, but dexcom number seems more correct, I will do another meter check. Often I find the first meter check was off.

Edit to add…
I think prior discussions talked about guessing your BG before doing meter check. I do the same with dexcom, especially with calibrations. If my gut feeling BG is different than dexcom or meter BG, I will usually do multiple meter checks before deciding what my real BG is. And as Eric says, also take into account if currently level.

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We calibrate about once a day or so with the G5. Works well for us.

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@daisymae - What did the graph of the cgm look like for the first hour of the session right after you did the double finger-stick entry?

Reason for asking. If that happened to be a time of rapid increase/decrease then it could significantly impact all future numbers for that session.


when i started my sensor session on friday, all was perfect. i had a complete flat line and from my finger sticks i had the same. the cgm was perfectly accurate, and it continues to be very accurate. i have just had some wacky numbers on the cgm which i have had to recalibrate for. when i posted this thread, i was just curious how frequently you guys have had “off” waky numbers on their cgm; what is the norm for re-calibrations?

obviously, as i read the comments/responses it doent seem like others have gone through what i have experienced. it hasnt been a big deal; i just correct and move forward. just curious.

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DM, I, too, calibrate in the morning to get a good start on the day. I was pretty level overnight and had drifted up a little to 125 on my cgm. My finger stick was 140, probably went up a little faster than the cgm tracked. I also do a fingerstick sometime before going to bed to confirm the cgm reading and recalibrate if needed (before making any corrections).

thanks for that. i’ve just wondered do people find themselves calibrating at times other than when the cgm asked to be calibrated. i have been on my dex since last friday which makes it 4 days now. i have had to recalibrate about 3 times b/c of way way off wacky differences from my finger sticks. i always do a finger stick before any bolus. always. and thats when i have noticed the sensor being off…well, sometimes i get “false” lows, but i basically ignore those.

PS: i just did a finger stick and my BG was 103. my dex read 100. pretty darn good for accuracy!!

Yeah, I have done that but not if rapidly going up or down. You’ll get a feel for when it’s a one-off and when the sensor is failing or there is a placement problem.

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Good attitude. Sounds like you found the right way to handle it.


just wanted to add that my dex is getting more and more accurate as the week goes by.

thanks for your support!


It will probably be most accurate right when it expires.

Mine is always most accurate right before it falls off…

@Eric - Ours is the opposite. But only I think because if the sticky stops holding well then we put tape (Opsite Flexifix) over it. So we will run it until the data gets bad and either we stop trusting it or the data completely stops. We used to get 12 days from a G5 sensor but the last 2 months or so, it seems like we have been only able to run to about 6 or 7 days. Which is odd.

I was wondering if something was up with that specific lot of sensors. Last night we just switched to a new sensor from a new lot so it will be interesting to see if we go right back to 12 days on a sensor or if it still dies out on day 6 or 7.

In any event, we are hoping to switch to the G6 in about a month and a half. All the system components have been altered so we have no idea how long those sensors will last. One way to find out.

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Don’t know if it is a coincidence, but our last lot has been averaging 8 days or so, compared to 14 before.