Dexcom G6 Calibration

Have had my Dexcom G6 for a couple of months now - helps a lot! One quirk that I do not understand relates to calibration. Initially I always put in my sensor code when I change sensors. After a day I try to ‘refine’ the readings by finger-stick so they are a bit more accurate - but the calibration does not act as I expect that it would. Let’s say my G6 reads 140 and my finger stick reads 100. If I calibrate on the receiver using 100 the G6 will then start to immediately read about 120 (NOT 100) on the receiver. If I want it to read 100 then I seem to need to put in a much lower value - say 80 - then it reads closer to 100; however, sometimes it just reverts back to a higher reading on the receiver after a few minutes. Maybe someone can explain this quirk to me. Many thanks. PS - this is not a deal-killer for me - just an unexplained quirk. I really like my Dexcom G6.

If you enter the same number twice, the Dexcom will calibrate to that number. Not sure that is great advice but that is how it works.

I have to calibrate almost every G6 sensor on the first day. My rules are to never calibrate more than 40 points at a time and never calibrate more than 50% of the difference. I use the 15 minute rule where I enter one calibration, wait 15 minutes and enter another calibration. And so on if needed. If I calibrate too much on the first day, I often have to calibrate on the second day to correct the rebound. But after that, my sensors work great until they expire at Day 10.

For sure I have no understanding of how the sensor reacts to calibrations and it has always bugged me that it picks an intermediary number. Though often if eventually moves up to what I calibrated.


I almost never calibrate anymore. I just go with it and it’s usually close enough. When I do check it, I find it’s never way off.

Remember the finger stick meter is also not perfect so you are calibrating and imperfect device with an imperfect device.

The dexcom calibrates the way it does because it has a built in calibration. That’s why it divides the difference between the internal cal and the cal you entered with finger stick.

Yes it keeps going back to that number no matter what you do.
If you are at 200 and it reads 180 Then it averages at 190.

If you wait 5 min and calibrate again. The finger stick is now 160 but dexcom says 180 you are now at 170 post calibration.

If you keep doing that, you will confuse it and it will shut down to that dreaded screen where it needs to start a mini warm up again.

But guess what, after it does that, it resets to the internal calibration again.

I find they work fine they way they are, if it’s way off, I toss it and start a new one.
but if you really don’t like that, you should use no code and calibrate twice a day.

Then you are not fighting that internal calibration.

Ladde I do the same. Even though there is some difference between real blood and interstitial fluid. I to enter the Glucometer data twice , but the match up is usually is sort lived They will usually drift apart again. I also don’t enter cal data if it’s less then 5 mg/dL

It’s the way the Dexcom algorithm works. It’s a combination of every it thinks you are based on the rate of change it tracks and the previous 2 readings. (That 3 value algorithm makes a lot of other things make sense when you understand this, like why the transmitter needs no communication for 3 cycles - 15 minutes - to restart a sensor) The number you enter is just 1 factor in the equation, but it also takes into account where you were before. The math does favor the calibration value, though. Also, the next reading will usually cover the rest of the distance, barring any change it detected since the fingerstick.

I don’t seem to have any bad numbers on the first day after starting a sensor. I guess some do, but mine read accurate enough to go by. I only calibrate if things are wonky?!?

I went through a period of time where I didn’t need to calibrate at all. Then, I started to get really off readings for the first day. I’ve since moved my sensors to my arms, rather than my abdomen and for some reason, I’m getting far more accurate readings the first day. I’m calibrating once or twice now, compared to 6 - 10 before. One Dexcom technician told me to calibrate every 15 minutes until I was within the acceptable difference range, but another told me that the more I calibrate, the more confused the sensor gets. I really hope the day comes when they are reliably accurate from the first reading.

1 Like

Many thanks to all for the feedback and the tips. Far more complicated than I originally had assumed - but good to know. Dimond.

I like to get my sensor within 5 points of accuracy. A brand new sensor takes more work to do that with. A new sensor starts low, a restarted sensor starts high.

On a new sensor I calibrate at the start or within 3 hours, let it go another couple of hours (or more) and calibrate it again. At that point one thing I notice is a new sensor will still trend down The next day it will have me too low again although closer to accuracy. So the next day if it says I am at 70, but I am at 80, I will enter 90 to get it to say 80. Then it will trend up to 85. That is where I like mine, within 5 points above what I am at.
But some need more work, and at this point after a day I can input the number twice to make it take what I want. But I wait at least 24 hours usually to do that as otherwise it’s algorithm won’t let it keep that number. And then at about day 3-5 I will check it a few times to make sure it’s staying accurate. Until restart time!

It’s worth it to me to put in the extra work and know when I am dosing that I really am within 5 points of what it reads.