T1D glossary

Time below range (TBR)

Also called time in hypoglycemia, time low.

Time below range is the share of CGM values under 70 mg/dL (3.9 mmol/L). The consensus splits it in two: level 1 is 54 to 69 mg/dL (3.0 to 3.8 mmol/L) and level 2 is under 54 mg/dL (3.0 mmol/L). The consensus puts reducing TBR first, before raising time in range. (International consensus on time in range, 2019)

Target

Under 4% of the time below 70 mg/dL (3.9 mmol/L), about 1 hour a day, and under 1% below 54 mg/dL (3.0 mmol/L), about 15 minutes a day. For older adults, under 1% below 70 mg/dL. (ADA Standards of Care 2026, section 6; International consensus on time in range, 2019)

Formula

TBR (%) = CGM values under 70 mg/dL ÷ all CGM values × 100

Worked example

Over 14 days, 121 of 4,032 values under 70 mg/dL is 3.0% TBR, about 43 minutes a day. If 20 of those 121 are under 54 mg/dL, the level 2 share is 0.5%.

Related terms

• Level 1 hypoglycemia
• Level 2 hypoglycemia
• Time in range
• Glycemia Risk Index

Sources, quoted

• International consensus on time in range, 2019: “Time below range (TBR): % of readings and time 54–69 mg/dL (3.0–3.8 mmol/L) Level 1”
• International consensus on time in range, 2019: “Time below range (TBR): % of readings and time <54 mg/dL (<3.0 mmol/L) Level 2”
• International consensus on time in range, 2019: “In both approaches, the first priority is to reduce TBR to target levels and then address TIR or TAR targets.”
• ADA Standards of Care 2026, section 6: “A goal percent time <70 mg/dL (<3.9 mmol/L) of <4% (or <1% for older adults) and a goal percent time <54 mg/dL (<3.0 mmol/L) of <1% are recommended in people using CGM to prevent hypoglycemia.”
• International consensus on time in range, 2019: “When applying the CGM metrics in clinical practice, it may be more meaningful and motivating to communicate to people with diabetes the importance of working to reduce the time spent <70 mg/dL (<3.9 mmol/L) to less than 1 h per day and time spent <54 mg/dL (<3.0 mmol/L) to less than 15 min per day, rather than using <4% and <1%, respectively, as the goal.”

Every quote above is checked against its source page before each update of this site; last checked 2026-10-06. The worked example is our own arithmetic. This page explains a term; it is not advice for a person's treatment.