CGM is a genuine game-changer. It shows where your glucose is now, where it’s been, and where it’s heading. The result: faster learning, fewer surprises, and a better percentage of time in range (3.9-10.0 mmol/L or 70-180 mg/dL) — if you use the trends rather than chasing single numbers.
But,
Before starting, it’s worth understanding the CGM Black Swan.
Why? The first question should always be:
“Do I understand the risk of using CGM readings for insulin dosing — and is that risk the same for all CGMs?”
For some devices, the risk is well characterised and clearly acceptable. For others, it isn’t. That difference matters, and it should shape how much risk we’re willing to take.
Simple
If you’re already well-versed in CGM, go deeper here:
A CGM device is the most important part of the diabetes management kit. If you don’t have one yet, it’s time to talk with your diabetes team about getting access.
Deep
CGM glucose vs finger-prick glucose
This picture shows the difference between CGM interstitial glucose and finger-prick blood glucose measurements.
Key things:
The CGM reading is about 5 minutes behind the blood glucose reading, so they will never match exactly.
If in doubt, get the finger prick blood glucose meter out!
It’s important to always have access to a ISO-standard finger prick blood glucose meter, with in date test strips, and to follow good testing technique! Otherwise, as time goes on, you risk theCGM Black Swan.
The CGM continually reads glucose and updates the display every 5 minutes.
CGM trend arrows show where glucose is heading. Each CGM has its own arrow system, but they all communicate the same idea: where glucose is likely to be in ~10 minutes.
If you use mg/dL, keep this simple conversion in mind: 1.0 mmol/L = 18 mg/dL. Roughly:
Time in range (TIR) is usually defined as 4.0–10.0 mmol/L (70–180 mg/dL). This table shows that the higher your TIR, the better your daily energy and future health. But the time you spend managing diabetes also rises as TIR increases. It’s a balancing act.
The international target for time-in-range is 70%.
However, not all CGMs measure or report glucose in the same way. Some systems require closer to 75–80% time-in-range to deliver the same health benefit.
And remember: not all CGMs are equal when it comes to how time-in-range is calculated and reported.
You may even want to join the nerdy glucose management crew and aim for >80% TIR by fully implementingDynamic Glucose Management.
What matters is finding the sweet spot between time-in-range and quality of life.
That balance will change over time as new challenges and priorities come your way — and that’s exactly how it should be.
The goal isn’t rigidity; it’s adaptation. We adjust, we evolve.
Don’t over-stress it. Stay responsive, not perfectionist, and keep moving forward.
Practical
Don’t chase day-to-day perfection. Use CGM to learn your patterns, adjust one lever at a time, and aim for a sustainable TIR that matches your current life constraints.
