Setting clear, personal goals is one of the most important steps in successful T1D management. But before you can set meaningful goals, you need to understand the metrics that measure your glucose control. Think of these as the dashboard of your diabetes management — each gauge tells you something different and important.

The Core Metrics Explained

A1C (Hemoglobin A1C)

Your A1C measures average blood sugar over the past 2-3 months. It works by measuring how much glucose has attached to your hemoglobin (the protein in red blood cells). Because red blood cells live about 3 months, A1C gives you a "big picture" view.

• Expressed as a percentage
• General target: Below 7% for most adults (ADA 2026 guidelines)
• Some people may aim for below 6.5% if they can achieve it without significant hypoglycemia
• Your personal target may differ based on your situation, age, and hypoglycemia risk

The limitation: A1C is an average. An A1C of 7% could mean you spent most of your time around 154 mg/dL — or it could mean you swung wildly between 50 and 300 mg/dL. That's why we need more metrics.

GMI (Glucose Management Indicator)

GMI is an A1C estimate calculated from your CGM data. It uses your average sensor glucose over 14+ days to estimate what your A1C would be.

• Useful for tracking trends between lab A1C tests
• May differ from lab A1C by up to 0.5% (this is normal)
• Requires at least 14 days of CGM data with 70%+ active time

Time in Range (TIR)

This is the percentage of time your blood sugar stays within the target range of 70-180 mg/dL. Many endocrinologists now consider TIR the single most useful CGM metric.

• General target: Above 70% (that's about 16 hours and 48 minutes per day)
• Every 5% increase in TIR is clinically meaningful
• More time in range = better long-term outcomes and better daily quality of life

Time Above Range (TAR)

TAR tracks hyperglycemia in two tiers:

• Time above 180 mg/dL — target: less than 25% (under 6 hours/day)
• Time above 250 mg/dL (very high) — target: less than 5% (under 1 hour 12 minutes/day)

Persistent highs above 250 mg/dL are especially concerning because they accelerate the risk of long-term complications.

Time Below Range (TBR)

TBR tracks hypoglycemia, also in two tiers:

• Time below 70 mg/dL — target: less than 4% (under 58 minutes/day)
• Time below 54 mg/dL (very low) — target: less than 1% (under 15 minutes/day)

Safety is the top priority. Reducing lows is often more urgent than increasing TIR. Severe hypoglycemia can be immediately dangerous, while hyperglycemia causes damage over years.

Coefficient of Variation (CV)

CV measures how much your blood sugar swings — your glucose variability. A stable line hovering around 150 mg/dL has a low CV; a rollercoaster from 60 to 300 has a high one.

• Target: 36% or less (≤36%)
• Below 36% is considered "stable"
• Above 36% suggests significant glycemic variability that should be addressed

The Complete CGM Target Table (ADA 2026)

Here's the full picture — the recommended targets for most adults with T1D:

Scenario: Priya Reads Her First CGM Report

Priya, 28, was diagnosed with T1D six months ago. Her endocrinologist pulls up her first 14-day CGM report and walks through it with her:

• A1C (lab): 7.8%
• GMI (from CGM): 7.6% — close to her lab value, good CGM coverage
• TIR: 52% — she's in range about 12.5 hours per day
• TAR (>180): 38% — over 9 hours per day spent high
• TAR (>250): 8% — almost 2 hours per day very high
• TBR (<70): 3% — under the 4% target, which is good
• TBR (<54): 0.5% — under the 1% target, also good
• CV: 41% — above 36%, indicating significant variability

Her doctor says: "Your lows are well-controlled — that's great. The main opportunity is reducing your time above 180. If we can bring your TAR down from 38% to under 25%, your TIR will naturally climb. Let's focus on post-meal spikes first."

Priya now has a clear picture: her priority is reducing highs, not worrying about lows. That's the power of understanding your metrics.

Quick-Reference: Reading Your CGM Dashboard

Use this checklist next time you open your CGM app's summary:

1. Check TBR first — Are you safe? (<4% below 70, <1% below 54)
2. Check TIR — Where are you now? What's your starting point?
3. Check TAR — Where are the highs? (>180 and >250 separately)
4. Check CV — Are you stable (≤36%) or on a rollercoaster (>36%)?
5. Check GMI — How does your estimated A1C track against your last lab?