Time in Range (TIR) is the percent of CGM readings within the target glucose range — typically 70 to 180 mg/dL — over a 14-day window. The international consensus target for most adults with type 1 or type 2 diabetes is greater than 70 percent. TIR is now considered a primary outcome alongside A1C in diabetes care.
How TIR Is Calculated
- Every 1 to 5 minutes, the CGM records a glucose value (the exact interval depends on the device).
- Over a defined window (usually 14 days), the software counts how many of those readings fall within 70 to 180 mg/dL.
- That count is divided by the total number of readings and expressed as a percent.
- Minimum 70 percent sensor wear (about 10 of 14 days) is required for the calculation to be reliable.
- Time below range (TBR) and time above range (TAR) are calculated similarly — they always sum to 100 percent with TIR.
The standard target range (70 to 180 mg/dL) was chosen by international consensus in 2019 — it captures the range where most short- and long-term harm is avoided.
Battelino 2019 Consensus Targets
| Population | Target Range | TIR Goal | TBR (<70) | TAR (>180) |
|---|---|---|---|---|
| T1D and T2D, non-pregnant adults | 70 to 180 mg/dL | >70% | <4% | <25% |
| Older or high-risk adults | 70 to 180 mg/dL | >50% | <1% | <50% |
| Pregnancy with T1D | 63 to 140 mg/dL | >70% | <4% | <25% |
| Pregnancy with T2D or GDM | 63 to 140 mg/dL | >85% | <4% | <10% |
The lower target (greater than 50 percent) for older or high-risk adults reflects the trade-off between glucose control and hypoglycemia risk — a hypo event in an older adult is far more dangerous than mild hyperglycemia.
Time Below Range and Time Above Range
| Metric | Threshold | Target | Clinical Meaning |
|---|---|---|---|
| TBR level 1 | <70 mg/dL | <4% (about 1 hour/day) | Mild hypoglycemia |
| TBR level 2 | <54 mg/dL | <1% (15 min/day) | Clinically significant hypoglycemia |
| TAR level 1 | >180 mg/dL | <25% (6 hours/day) | Mild hyperglycemia |
| TAR level 2 | >250 mg/dL | <5% (about 1 hour/day) | Significant hyperglycemia; complications risk |
TBR is the safety metric. A high TIR achieved with elevated TBR (frequent lows) is not a safe configuration. Reduce TBR first, then push TIR higher.
TIR vs A1C: Rough Conversion
| TIR (%) | Mean Glucose (mg/dL) | Approximate A1C (%) |
|---|---|---|
| 90 | 140 | 6.5 |
| 80 | 155 | 7.0 |
| 70 | 170 | 7.5 |
| 60 | 185 | 8.0 |
| 50 | 200 | 8.5 |
| 40 | 215 | 9.0 |
Each 10 percent increase in TIR is roughly equivalent to a 0.5 percent decrease in A1C. The relationship is not exact — variability matters. Two people with the same TIR can have different mean glucose and different A1C if one has more swings.
Why TIR Matters Independently of A1C
- Captures variability: someone with average glucose 170 mg/dL but swinging 60 to 280 has the same A1C as someone steady at 170, but very different physiology.
- Captures hypoglycemia: A1C cannot detect lows; TBR can.
- Predicts complications: Beck and colleagues re-analyzed the DCCT/EDIC trial and found TIR independently predicts retinopathy and microalbuminuria.
- Patient-actionable: a daily TIR percent is easier to act on than a quarterly A1C number.
- Faster feedback: 14-day window vs 3-month window.
When to Use TIR
- Anyone using a CGM — automatically calculated in AGP reports.
- Type 1 diabetes — primary tracking metric alongside hypoglycemia frequency.
- Type 2 diabetes on insulin or sulfonylurea — captures lows A1C misses.
- Pregnancy — when tight control is needed and quick feedback matters.
- Hospital and post-hospital periods — when therapy adjustments happen rapidly.
- Hemoglobinopathies — when A1C is unreliable.
- Anemia, recent transfusion, EPO use — when A1C is biased.
How to Improve TIR
| Strategy | Typical TIR Impact |
|---|---|
| Consistent meal timing and carb counting | +10 to 15% |
| Pre-meal insulin timing (15 min before) | +5 to 10% |
| Automated insulin delivery (AID) | +10 to 20% |
| Lower-carb / lower-GI diet | +10 to 15% |
| Post-meal walking (10 to 20 min) | +5 to 10% |
| Address dawn phenomenon | +3 to 8% (overnight) |
| Reduce overnight hypoglycemia | +5 to 10% (and safer) |
Common TIR Patterns and What They Mean
- Low TIR, high TAR, low TBR: too much hyperglycemia — increase insulin, reduce carbs, add medication.
- Moderate TIR, high TBR: overcorrecting — reduce insulin doses, adjust basal rate.
- Low TIR, high TAR and TBR: high variability — focus on consistent timing, AID, smaller meal carbs.
- High TIR, low TBR: well controlled — maintain.
- Stable TIR but rising A1C: check for hemoglobinopathy or CGM sensor bias.
Limitations of TIR
- Requires CGM use with adequate sensor wear (≥70 percent).
- Does not directly measure variability (CV or MAGE do that).
- Reference range (70 to 180) is standardized; some clinicians use tighter ranges (e.g., 70 to 140).
- Sensor accuracy declines in the first 24 hours and at extremes of glucose.
- Not all insurance covers CGM for type 2 diabetes not on insulin.
- 14-day snapshots may miss longer-term patterns.
Related CGM Metrics
TIR is one of several CGM metrics that work together. See GMI vs A1C, coefficient of variation for glucose, MAGE and glucose variability, and the Ambulatory Glucose Profile. For background on glucose averages and A1C, see A1C levels.
The Bottom Line
Time in Range is the percent of CGM readings within 70 to 180 mg/dL over a 14-day window. Target greater than 70 percent for most adults; greater than 50 percent for older or high-risk patients; tighter for pregnancy. Always interpret TIR alongside Time Below Range (target less than 4 percent below 70) and Time Above Range. Roughly, every 10 percent gain in TIR equals about 0.5 percent A1C reduction. TIR captures variability and hypoglycemia that A1C misses and predicts complications independently. If you wear a CGM, look at your TIR weekly — it is the most actionable single number in modern diabetes care.
