Hemoglobin A1c (often just called A1c) is a blood test that reflects your average blood sugar over the past two to three months. Estimated average glucose, or eAG, is simply that A1c number translated into the same units you see on a home glucose meter, typically mg/dL. Together, they give you two ways of looking at the same information: A1c as a percentage, eAG as a daily glucose number you can actually picture.
How A1c Forms in Your Blood
Glucose in your bloodstream naturally sticks to hemoglobin, the protein inside red blood cells that carries oxygen. The process happens in two steps: glucose first loosely attaches to one end of the hemoglobin molecule, then undergoes a chemical rearrangement that locks it in place permanently. Once attached, it stays for the remaining life of that red blood cell.
Red blood cells live roughly 120 days. Older cells have had more time to accumulate glucose, so they carry a higher glycated fraction than younger cells. When a lab measures your A1c, it samples red blood cells of all ages circulating at that moment and reports the overall percentage of hemoglobin with glucose attached. A higher percentage means your blood sugar has been running higher, on average, over the previous two to three months.
What eAG Is and Why It Exists
An A1c of 7% doesn’t tell most people much on its own. Estimated average glucose converts that percentage into a number that looks like a regular blood sugar reading. If you’re used to seeing values like 130 or 180 mg/dL on your meter, eAG puts your A1c into that same language.
The conversion comes from a large study called ADAG, which tracked 507 adults wearing continuous glucose monitors and doing frequent finger sticks over three months, then compared their average glucose to their lab A1c. The correlation was strong (r = 0.92), and the American Diabetes Association now recommends that labs report eAG alongside A1c on every result.
The Conversion Formula
The formula linking the two is straightforward:
eAG (mg/dL) = 28.7 × A1c − 46.7
For those using international units: eAG (mmol/L) = 1.59 × A1c − 2.59.
Here’s what that looks like across a practical range of A1c values:
- A1c 5.0% → eAG of about 97 mg/dL
- A1c 5.7% → eAG of about 117 mg/dL (prediabetes threshold)
- A1c 6.0% → eAG of about 126 mg/dL
- A1c 6.5% → eAG of about 140 mg/dL (diabetes diagnostic threshold)
- A1c 7.0% → eAG of about 154 mg/dL
- A1c 8.0% → eAG of about 183 mg/dL
- A1c 9.0% → eAG of about 212 mg/dL
- A1c 10.0% → eAG of about 240 mg/dL
- A1c 12.0% → eAG of about 298 mg/dL
Each full percentage point of A1c corresponds to roughly a 29 mg/dL change in eAG. That gives you an easy mental shortcut: dropping your A1c by one point means your average blood sugar fell by about 29 mg/dL.
What the Numbers Mean for You
The American Diabetes Association’s 2025 standards set an A1c goal of less than 7% (eAG below 154 mg/dL) for most nonpregnant adults with diabetes who aren’t experiencing frequent or severe low blood sugar episodes. That target is tied to significantly lower rates of diabetes complications affecting the eyes, kidneys, and nerves.
For day-to-day context, the ADA also recommends fasting glucose between 80 and 130 mg/dL and post-meal peaks below 180 mg/dL. Your eAG sits somewhere in between those daily highs and lows, representing the overall average. A person with an eAG of 154 mg/dL will still have readings well above and below that number throughout the day. The eAG helps you see the big picture that individual finger sticks can miss.
eAG vs. GMI on a Continuous Glucose Monitor
If you wear a continuous glucose monitor (CGM), you may see a number called the glucose management indicator, or GMI. This is calculated from your CGM’s average glucose readings over 14 or more days. It looks a lot like eAG, and it’s designed to approximate what your lab A1c might be.
However, GMI and lab-based eAG often don’t match perfectly, and that’s expected. Lab A1c depends on how glucose physically attaches to hemoglobin inside your red blood cells, and that process varies from person to person. Some people’s red blood cells glycate more readily; others’ cells live slightly longer or shorter than average. These biological differences mean two people with identical average glucose levels can have different lab A1c results. GMI, by contrast, is based purely on the glucose numbers your sensor reads in the fluid under your skin.
A gap between your GMI and your lab A1c isn’t necessarily a problem. It just means the two measurements are capturing different things. Your healthcare team can use both to build a fuller picture of your glucose control.
When A1c and eAG Can Be Misleading
Because A1c depends on hemoglobin inside red blood cells, anything that changes how long those cells survive or how hemoglobin behaves will skew the result, and the eAG calculated from it.
Iron deficiency anemia is one of the more common culprits. When your body is low on iron, red blood cells can live longer than usual, giving glucose extra time to attach. This pushes A1c artificially higher, making blood sugar control look worse than it actually is. The effect is well documented in both pregnant and nonpregnant women.
Other conditions that affect A1c accuracy include:
- Hemoglobin variants (such as sickle cell trait or thalassemia), which can interfere with certain A1c lab methods or change how readily glucose binds.
- Hemolytic anemia, where red blood cells are destroyed faster than normal. Shorter cell lifespans mean less time for glycation, so A1c reads falsely low.
- Recent significant blood loss or transfusion, which floods the circulation with newer red blood cells and lowers the measured A1c.
- Pregnancy, which naturally increases red blood cell turnover and can make A1c less reliable, especially when iron deficiency is also present.
If any of these apply to you, your lab A1c (and by extension, your eAG) may not accurately reflect your true average glucose. In those situations, direct glucose monitoring through a meter or CGM gives a more reliable day-to-day picture.
Putting A1c and eAG to Practical Use
The most useful thing about eAG is that it lets you compare your lab result to what you’re seeing at home. If your meter average over the past three months is around 160 mg/dL and your eAG comes back at 154 mg/dL, those numbers line up well. If there’s a large gap, it could signal that you’re missing high or low readings (perhaps overnight spikes your meter doesn’t catch) or that a biological factor is shifting your A1c.
Tracking eAG over time also makes progress more tangible. Knowing your average dropped from 183 to 154 mg/dL feels more concrete than hearing your A1c went from 8% to 7%. It’s the same improvement, just expressed in units that connect to your daily experience with a glucose meter.