Daily calibration of Dexcom G6

I just got the Dexcom 6 days ago. I pre soaked the sensor for 12 hours and then fired it up. Nearly every day, I have had to re calibrate the sensor. Today I had to do it twice. It had me at 240 (finger stick at 206) and two hours later it had me at 55 (finger stick 124). Other days I’ve had to re calibrate.
Am I doing something wrong? I expected to calibrate (maybe) the first 24 hours.

I’m not sure if you’ve tried to calibrate it twice yet? It picks a number between your calibration and it’s reading, which still can be off by a lot. So a second calibration will bring it closer to the number you actually want.

Plus it’s always off more at the higher numbers, I always wait to calibrate it at the number I want to be at the most. So I aim for 95 and I don’t calibrate it until I am 95-105. And then I only compare it’s accuracy when I am close to those numbers.


I really rarely calibrate mine. The only time I have trouble is if it bleeds a lot. So no, you shouldn’t have to calibrate like you have been. It may be in a bad spot?

I typically calibrate once at most per sensor (if it’s “close enough” I don’t calibrate at all).

Yes there are times when they don’t agree but calibrating each and every time they don’t agree seems counterproductive. For example you calibrated “down 36” the first time then you found two hours later the that the meter was “down”.

I personally don’t think the difference between 240 and 206 is a big deal. But I do think the difference between 55 and 124 is a big deal.


It’s also possible that your hand held meter is off. Just throwing that out there in case you didn’t have enough things to worry about yet!!

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did you enter the sensor code to start? if you dont enter a sensor code when you start a new one it will make you calibrate daily or every 12 hours

I’ll check that but when the g6 said 55 I felt fine

I did put in a sensor code. My first ever sensor may be a dud!

On my stomach. Not near naval or waistband of pants

My two cents, is that your first calibration probably wasn’t necessary.

Your bg was falling when the fingerstick said 206 because two hours later the fingerstick said 124.

You have to remember there’s a lag intrinsic to any CGM of 15 minutes or more.

When the CGM read 240, that may have been correct for your bg about 15-20 minutes earlier. So you told the meter to read lower and later on it read lower.

I’m not sure I would ever calibrate for 240 vs 206. No they are not numerically the same. But I like to calibrate when my bg is relatively “flat” and not changing to take out the gotcha of the 15 minute CGM delay.

If I notice that several consecutive mid-range bg’s (say 80-150) are different between meter and CGM, always in the same direction, then I will calibrate.


I to only calibrate when my BS is not falling or rising. I usually have to calibrate once about 2 hours after the first reading.

I have completely given up calibration, I find that it does nothing but for the five min after you calibrate.
My sensors are generally spot on. Even at the start. I soak a few hours before, but sometimes I just stick it on and go.

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Same here.

Now I’m jealous lol…When I start a brand new one it is always big time lower…and when I do a restart it is big time higher lol…

It screws with my time in range so I pounce on it as soon as it starts and calibrate it.

The general rule of thumb for the G6 is the 20/20 rule.

According to the graph from dexcom you should not have tried to calibrate the 240 dexcom reading down to your finger stick 209 as it was within their range of accuracy. I also use @Marie20’s practice of not calibrating until I’m within the range that I need it to be most accurate (for me this is from 75 to 150 mg/dl).


Yep. I calibrate as frequently as necessary, which isn’t often… Unless it’s a sucky sensor. It’s usually good the first day. Sometimes goes off by the end of a session. It ALWAYS comes back high after a restart, though. I try to make sure I’m around 100 when the sensor warmup finishes, because it’s going to read 160-200ish.

I do follow simple calibration rules, though:

  1. Only calibrate when in range. There’s a margin of error in both the glucometer and CGM, and the bigger the number, the higher the discrepancy.

  2. I only calibrate when my trend is flat, and never after recently eating and/or bolusing, since it’s likely my glucose is changing but not registered on the CGM yet.

  3. Never try to enter a calibration that is more than 50% different. After a restart, when I get the crazy high Dexcom readings, I’ll actually split the difference between two different calibrations spaced at least 15 minutes apart. Otherwise, the sensor gets crabby.

@Robyn_H If it gets crabby, I’m assuming you mean it keeps asking for calibrations and won’t stop? Try 2 calibrations with the same number within a couple of minutes. It seems to pacify it right away! Someone on here mentioned that once, sorry I don’t remember who and it works great!

Like you the sweet spot to a restart is around 80-100 because of that initial high reading on a restart.


I also only wear mine on my stomach, but sometimes I hit scar tissue or something funky that makes it not work as well. Just a thought.

This is very helpful and wasn’t in the mini user guide that I got with my Dexcom order. I have requested the entire, full sized user guide from Dexcom.

good to know