What Is Time-in-Range — And Why It Matters More Than HbA1c
HbA1c tells you your average glucose over three months. Time-in-Range tells you what your glucose is actually doing — every hour of every day. Here's why that distinction matters enormously.
The problem with HbA1c alone
For decades, HbA1c — the glycated haemoglobin test that reflects your average blood glucose over roughly three months — was the primary measure of diabetes management. A target of below 7% (53 mmol/mol) became the gold standard that clinicians and patients alike chased.
But HbA1c has a fundamental limitation: it's an average. Two people can have identical HbA1c readings while living entirely different glycaemic lives. One might spend most of their time comfortably in range, with rare mild excursions. Another might swing between severe hypoglycaemia and significant hyperglycaemia, with the peaks and troughs averaging out to the same number. The HbA1c can't tell the difference.
What is Time-in-Range?
Time-in-Range (TIR) is the percentage of time that your glucose stays within a defined target range — typically 3.9 to 10.0 mmol/L (70–180 mg/dL) for most adults with Type 1 or Type 2 diabetes, based on international consensus guidelines published in 2019.
A continuous glucose monitor (CGM) takes a reading every 5 minutes — that's 288 readings per day. TIR calculates how many of those readings land within your target band, expressed as a percentage. A TIR of 70% means your glucose was within range for 16.8 hours out of every 24.
International consensus targets (adults with Type 1 or Type 2 diabetes)
- Time-in-Range (3.9–10.0 mmol/L): >70%
- Time Below Range (<3.9 mmol/L): <4%
- Time Below Range (<3.0 mmol/L — severe hypo): <1%
- Time Above Range (>10.0 mmol/L): <25%
- Time Very High (>13.9 mmol/L): <5%
Why TIR has become the primary CGM metric
Several landmark studies have established a strong relationship between TIR and the outcomes that matter most in diabetes management:
- A 10 percentage point improvement in TIR correlates with approximately a 0.5% reduction in HbA1c.
- Every 10% increase in TIR is associated with a 6% reduction in the risk of diabetic retinopathy progression.
- Lower TIR is significantly associated with increased markers of cardiovascular risk.
- For people with Type 1 diabetes, TIR is a stronger predictor of microvascular complications than HbA1c alone in several cohort studies.
The practical implication: TIR gives you a daily feedback loop. HbA1c arrives three months after the fact, by which point the damage is done. TIR lets you respond to patterns in real time — which is exactly what a CGM is designed to enable.
TIR in GlucoHome
GlucoHome calculates your Time-in-Range in real time from your Dexcom data and displays it in multiple ways: as a percentage summary on your main dashboard, as a donut chart breaking out time-in-range, time-below-range, and time-above-range, and as a trend over days, weeks, and months so you can see whether your management is improving.
You can customise your target range to match your prescribed thresholds — GlucoHome uses your configured range for all TIR calculations. That's important because different patients have different targets: tighter ranges are appropriate for some people and more liberal targets for others (for example, during pregnancy or in elderly patients where hypoglycaemia risk is a primary concern).
TIR, Time Below Range, and hypoglycaemia
One of TIR's most important contributions is making hypoglycaemia visible. HbA1c can mask hypoglycaemia — if you're having frequent lows that are being corrected with fast carbohydrates, the highs and lows can average out to a deceptively "good" HbA1c. TIR exposes this by separately reporting time below range.
GlucoHome's Time-in-Range chart segments your glucose time into all five clinically recognised bands, so you can see not just your overall TIR but specifically how much time you're spending in dangerous low-glucose territory — information that's critical for anyone managing insulin, particularly Type 1 patients.