TempoLife › Features › Blood sugar explained › cgm
Continuous glucose monitors (CGM) — reference ranges
A small sensor under the skin reads glucose every few minutes and draws the whole curve — not just the moments you prick. A different picture: shape, not points.
| Band | mmol/L | mg/dL | What it means |
|---|---|---|---|
| Time in range | 3.9-10.0 mmol/L | 70-180 mg/dL | The international consensus target: for most adults with diabetes, at least 70% of the day inside this band. |
| Below range | under 3.9 | under 70 | The consensus target is under 4% of the day below 3.9 mmol/L, and under 1% below 3.0. |
| Above range | over 10.0 | over 180 | The consensus target is under 25% of the day above 10 mmol/L. |
Reading it in context
For someone without diabetes, a CGM mostly shows a flat line between 4 and 7.8 mmol/L with modest, brief bumps after meals. The useful habits the curve exposes: which meals spike and crash, what a walk after eating does to the peak, and what alcohol does to the overnight line.
The sensors read the fluid between cells, not blood, so they lag blood glucose by 5-15 minutes and read lower during rapid change — when the trend arrow points down, the real blood value is usually lower than the screen. Finger-prick checks stay the reference for decisions.
A CGM is a trend tool, not a diagnostic one: the wearer's own clinician sets the targets, and the consensus time-in-range numbers above are for adults with diabetes, not a scorecard for healthy wearers.
When to see a clinician
- CGM values repeatedly above 11 mmol/L or below 3.9 — bring the report, not just the feeling, to a clinician.
- A hypo with a flat or rising arrow that stays low despite treatment — treat first, review after.
Reference only, not a diagnosis. The thresholds on this page are population-level WHO and ADA values; your clinician interprets your own numbers against your history, medicines and other tests. If a value comes with symptoms, or keeps moving in the wrong direction, that is the signal to act on — not this page.