Time in Range vs. A1C: Why endocrinologists are changing their focus

For decades, the Hemoglobin A1C test was the undisputed gold standard of diabetes control. You went to the clinic every three months, gave some blood, and that single percentage dictated whether you were doing a "good job" or a "bad job."

Today, top endocrinologists and organizations like the American Diabetes Association (ADA) are heavily promoting a far more actionable and realistic metric: Time in Range (TIR).

What’s wrong with A1C?

A1C is an average. It measures how much glucose has attached to your red blood cells over a 90-day period. The problem with averages is that they completely hide the extremes.

Imagine two people living with diabetes, both with an A1C of 7.0%.

Person A: Their glucose fluctuates wildly, dropping to 40 mg/dL at 3 AM and rocketing to 300 mg/dL after lunch. Their mathematical average comes out to a "good" A1C, but their daily quality of life is severely impacted by exhaustion, brain fog, and the emotional toll of the glycemic rollercoaster.

Person B: Their glucose remains steady, gently rolling between 80 and 160 mg/dL.

An A1C blood test treats both patients as if they have identical health outcomes. Your body knows that isn't true.

The power of Time in Range (TIR)

Time in Range, made possible by the widespread adoption of Continuous Glucose Monitors (CGMs) like Dexcom and FreeStyle Libre, measures the exact percentage of the day you spend inside your target zone (typically defined as 70-180 mg/dL).

The international clinical consensus states that a solid initial goal for most people with type 1 or type 2 diabetes is:

• More than 70% of the time in range (70-180 mg/dL).
• Less than 4% of the time below range (hypoglycemia, under 70 mg/dL).

Visualizing daily success

The biggest psychological benefit of TIR is that it breaks the punishing cycle of the quarterly A1C test. If you had a tough day and hit 40% in range because pizza math is hard, you get to wake up tomorrow with a fresh slate and aim for 80%.

Companion apps like Dulce bring this metric to the forefront of your daily experience. By placing trend lines and TIR calculations right on your iPhone lock screen widgets and Apple Watch face, you stop guessing how the day is going and start making proactive, micro-adjustments.