Convert your HbA1c (A1C) test result into an estimated average glucose (eAG) reading in mg/dL or mmol/L, and see the corresponding ADA diagnostic category.
A1C (HbA1c) reflects your average blood glucose over roughly the past two to three months, measured as the percentage of red blood cells carrying glucose-coated haemoglobin. eAG (estimated average glucose) translates that percentage into the same mg/dL or mmol/L units your glucose meter uses, so the number is easier to relate to day-to-day readings. An A1C of 5.5% works out to an eAG of about 111 mg/dL (6.2 mmol/L).
⚕️ Medical Notice: eAG is a mathematical estimate only. Conditions affecting red blood cells — including anaemia, certain blood disorders, a recent blood transfusion, kidney disease, and pregnancy — can make A1C results inaccurate and throw off the eAG conversion. Always confirm results and their meaning with your doctor.
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eAG is calculated directly from your A1C percentage using a linear formula derived from the ADAG (A1c-Derived Average Glucose) study, which correlated continuous glucose monitoring data with A1C results across a large group of participants. The relationship was published by Nathan DM et al. in Diabetes Care (2008) and is the formula adopted by the American Diabetes Association.
The American Diabetes Association (ADA) uses A1C thresholds to classify results into normal, prediabetes, and diabetes ranges. The approximate eAG figures below are calculated using the same formula, at the boundary of each A1C range.
| Category | A1C Range | Approx. eAG (mg/dL) | Approx. eAG (mmol/L) |
|---|---|---|---|
| Normal | Below 5.7% | Below 117 mg/dL | Below 6.5 mmol/L |
| Prediabetes | 5.7% – 6.4% | 117 – 137 mg/dL | 6.5 – 7.6 mmol/L |
| Diabetes | 6.5% or above | 140 mg/dL or above | 7.8 mmol/L or above |
Because A1C measures glucose attached to red blood cells, anything that changes red blood cell lifespan or count can shift the result away from your true average glucose:
A1C (also called HbA1c or glycated haemoglobin) is a blood test that measures the percentage of your red blood cells that have glucose attached to their haemoglobin. Because red blood cells live for about three months, A1C gives a picture of your average blood glucose over that period, rather than a single snapshot like a finger-prick reading. eAG (estimated average glucose) simply expresses that same A1C percentage as an average glucose number in mg/dL or mmol/L, the same units shown on a home glucose meter — making it easier to relate your A1C to the day-to-day numbers you may already track.
The eAG formula was developed from the ADAG (A1c-Derived Average Glucose) study, a large multi-centre study that fitted continuous glucose monitors and frequent self-testing meters to hundreds of participants over several months, then compared their measured average glucose to their lab A1C result. The resulting linear relationship — eAG (mg/dL) = 28.7 × A1C(%) − 46.7 — was published by Nathan DM and colleagues in Diabetes Care in 2008 and was subsequently adopted by the American Diabetes Association as the standard way to report eAG alongside A1C results.
Because eAG is a statistical average derived from population data, your own personal average may differ slightly from your calculated eAG — some people run a little higher or lower than the formula predicts for the same A1C, partly due to individual differences in red blood cell lifespan. eAG is best used as a helpful translation of your A1C, not as a substitute for your actual meter or continuous glucose monitor readings, which reflect your specific day-to-day pattern.
What is A1C and what does it measure?
A1C (HbA1c) is a blood test that measures the percentage of red blood cells carrying glucose-coated haemoglobin. Because red blood cells live for around three months, A1C reflects your average blood glucose level over roughly the past 2-3 months, rather than a single moment in time like a finger-prick glucose reading.
What is eAG (estimated average glucose)?
eAG stands for estimated average glucose. It translates your A1C percentage into the same mg/dL or mmol/L units used on a glucose meter, making it easier to relate your A1C result to the everyday glucose numbers you may already be tracking.
How is eAG calculated from A1C?
eAG is calculated using the formula eAG (mg/dL) = 28.7 × A1C(%) − 46.7, which can then be divided by 18.0182 to convert to mmol/L. This formula comes from the ADAG (A1c-Derived Average Glucose) study, published by Nathan DM et al. in Diabetes Care (2008), which compared continuous glucose monitoring data with A1C results.
What A1C level is considered normal, prediabetic, or diabetic?
According to the American Diabetes Association, an A1C below 5.7% is considered normal, 5.7% to 6.4% is classified as prediabetes, and 6.5% or above is classified as diabetes. These thresholds apply to a laboratory A1C blood test interpreted by a doctor.
Why might my eAG not match my glucose meter average?
eAG is based on a population-level statistical relationship between A1C and average glucose, so individual results can vary. Differences in red blood cell lifespan, testing frequency, and the times of day you check your glucose can all mean your personal average differs slightly from the calculated eAG.
Can conditions like anaemia affect my A1C result?
Yes. Anaemia, certain blood disorders, a recent blood transfusion, kidney disease, and pregnancy can all affect red blood cells in ways that make A1C — and therefore the eAG calculated from it — less accurate. If you have any of these conditions, discuss the best way to monitor your glucose with your doctor.
How often should A1C be tested?
For most people without diabetes, A1C is checked as part of routine screening as advised by a doctor. People with diabetes are commonly tested every 3 to 6 months, though your doctor may recommend a different schedule depending on how well your glucose levels are controlled.
Is eAG the same as a fasting blood glucose reading?
No. eAG is an estimate of your overall average glucose across day and night, derived from your A1C. A fasting blood glucose test only measures your glucose level at one point in time, after not eating for several hours, so the two numbers measure different things and are not directly interchangeable.
What is the ADAG study behind the eAG formula?
The ADAG (A1c-Derived Average Glucose) study was a large research project that fitted participants with continuous glucose monitors and frequent self-testing over several months, then compared their measured average glucose with their A1C results. The resulting formula was published by Nathan DM et al. in Diabetes Care (2008) and is used by the American Diabetes Association to report eAG.
Can I use this calculator to diagnose diabetes myself?
No. This calculator provides an educational estimate only and cannot diagnose prediabetes or diabetes. A diagnosis requires a laboratory A1C or blood glucose test interpreted by a qualified healthcare professional, often confirmed with a repeat test. Always speak with your doctor about any concerns regarding your results.