Hemoglobin A1C vs Time in Range: Which Matters More?

Understanding the Two Key Metrics in Diabetes Management

For decades, the hemoglobin A1C test was the gold standard for measuring blood sugar control in people with diabetes. But with the rise of continuous glucose monitors (CGMs), a new metric called Time in Range (TIR) has emerged — and it's changing how doctors and patients think about diabetes management.

So which one matters more? The honest answer is: both do, but for different reasons. Understanding what each measures — and where each falls short — can help you and your healthcare team make smarter decisions about your care.

What Is Hemoglobin A1C?

The A1C test measures the percentage of hemoglobin in your blood that has glucose attached to it. Because red blood cells live for about 2–3 months, A1C gives a general picture of your average blood sugar over that time period.

• A normal A1C is below 5.7%
• Prediabetes falls between 5.7% and 6.4%
• A diabetes diagnosis is made at 6.5% or higher
• Most people with Type 2 diabetes aim for below 7%, while targets may vary for Type 1

A1C is widely available, inexpensive, and strongly linked to the risk of long-term complications such as kidney disease, neuropathy, and retinopathy. It remains a cornerstone of diabetes care worldwide.

What Is Time in Range?

Time in Range (TIR) refers to the percentage of time your blood glucose stays within a target range — typically 70 to 180 mg/dL (3.9 to 10.0 mmol/L) — over a given period, usually 14 days. This data is collected through a CGM device worn on the body.

General TIR goals recommended by diabetes organizations include:

• Above 70% TIR for most people with Type 1 or Type 2 diabetes
• Above 50% TIR for older adults or those at high risk of hypoglycemia
• Less than 4% time below range (under 70 mg/dL)
• Less than 1% time critically low (under 54 mg/dL)

Research has shown that higher TIR is associated with lower rates of diabetic complications, making it a clinically meaningful measure alongside A1C.

Where A1C Falls Short

Despite its usefulness, A1C has real limitations. Because it reflects an average, it can mask dangerous blood sugar swings. A person who frequently spikes to 250 mg/dL and crashes to 60 mg/dL might have the same A1C as someone whose glucose stays steady at 120 mg/dL all day — yet their risk profile is very different.

A1C can also be inaccurate in people with certain conditions like anemia, sickle cell trait, or kidney disease. Additionally, it gives no insight into when high or low blood sugars occur, making it harder to fine-tune treatment.

Where Time in Range Falls Short

TIR has its own limitations. It requires access to a CGM, which can be costly and isn't available to everyone. TIR data also needs to be interpreted carefully — different patients may have different target ranges depending on age, pregnancy status, or risk of hypoglycemia. Furthermore, TIR doesn't have the same long-term complication data that A1C has accumulated over decades of research.

Using Both Metrics Together

The smartest approach is to use A1C and TIR as complementary tools, not competing ones. Together, they paint a fuller picture of blood sugar control:

• A1C tells you the long-term average and helps predict complication risk
• TIR tells you about daily glucose variability, highs, lows, and patterns
• Discrepancies between the two can signal problems worth investigating

Major diabetes organizations, including the American Diabetes Association (ADA), now recommend incorporating TIR into clinical care — especially for people using CGMs.

The Bottom Line

Neither A1C nor Time in Range tells the complete story on its own. A1C remains essential for tracking long-term trends and assessing complication risk. Time in Range adds critical day-to-day context that A1C simply cannot provide. By using both, you and your doctor can build a more complete, personalized picture of your diabetes health — and make better decisions to protect your future.