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A1c to Average Glucose (eAG): Calculator + Conversion Chart

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Reviewed by: Martín Rodríguez (editorial policy ) · Last reviewed: Jun 4, 2026

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The estimated Average Glucose (eAG) is the mg/dL translation of your HbA1c, derived from the Nathan formula published in Diabetes Care in 2008: eAG (mg/dL) = 28.7 × A1c − 46.7. This regression came out of the A1c-Derived Average Glucose (ADAG) study and was formally endorsed by the American Diabetes Association the same year, with the goal of giving patients a number that maps onto the glucometer readings they actually see every day. For most people, a 7% A1c means a lot less than "about 154 mg/dL on average over the last 2–3 months" — eAG is clinically more intuitive than the percentage and reduces the educational gap during counseling. The conversion remains useful even in the CGM era: it lets you sanity-check whether a continuous glucose monitor's 14-day average lines up with the lab A1c, flag hemoglobinopathies or anemia when the two diverge, and decide whether fructosamine (a 2–3 week glycation marker on serum proteins) is a better short-term proxy. Understanding A1c-to-eAG conversion matters because it anchors patient education, medication titration, and shared decision-making for type 1 and type 2 diabetes.

Last reviewed: June 3, 2026 Verified by Martín Rodríguez Source: Nathan DM et al. Translating the A1C Assay Into Estimated Average Glucose Values. Diabetes Care 2008 (ADAG Study), American Diabetes Association — Standards of Care in Diabetes 2025, Bergenstal RM et al. Glucose Management Indicator (GMI) from CGM. Diabetes Care 2018, NIDDK — The A1C Test & Diabetes (NIH) 100% private

To convert A1c to estimated average glucose (eAG), use the ADA-endorsed Nathan 2008 formula: **eAG (mg/dL) = 28.7 × A1c − 46.7**. Quick reference: A1c 6% ≈ 126 mg/dL, 6.5% ≈ 140 mg/dL, 7% ≈ 154 mg/dL, 8% ≈ 183 mg/dL, 9% ≈ 212 mg/dL, 10% ≈ 240 mg/dL. A1c below 5.7% is normal, 5.7–6.4% is prediabetes, and 6.5% or higher meets the diabetes threshold.

When to use this calculator

Patient counseling: translate an A1c percentage into mg/dL the patient recognizes from their meter, improving adherence and self-management
Type 1 diabetes on CGM: compare GMI/CGM 14-day average against eAG from lab A1c — a >0.5% gap suggests hemoglobinopathy, recent transfusion, or iron-deficiency anemia distorting the A1c
Type 2 diabetes treatment escalation: contextualize an A1c of 8.5% (eAG 197 mg/dL) when deciding GLP-1 RA add-on, basal insulin start, or referral to endocrinology
Fructosamine fallback: in sickle cell trait, thalassemia, hemolytic anemia, or pregnancy, A1c is unreliable — fructosamine (2–3 week window) becomes the preferred glycation marker
Quality improvement and population health: stratify a diabetes panel by eAG bins (<154, 154–183, >183 mg/dL) to prioritize outreach

Example Calculation

HbA1c 6.5%
eAG = 28.7 × 6.5 − 46.7 = 140 mg/dL

Result: Diabetes range (≥6.5%) — eAG 140 mg/dL

How it works

2 min read

A1c → eAG conversion table (Nathan 2008)

HbA1c (%)	eAG (mg/dL)	95% CI (mg/dL)
5.0	97	76–120
5.5	111	89–135
6.0	126	100–152
6.5	140	111–169
7.0	154	123–185
7.5	169	135–202
8.0	183	147–217
8.5	197	158–234
9.0	212	170–249
10.0	240	193–282
11.0	269	217–314
12.0	298	240–347

Accuracy limitations

The Nathan ADAG regression has an R² of 0.84 and a coefficient of variation around 12%, meaning two patients with identical 14-day mean glucose can land in different A1c bins. Individual glycation rates vary — the Hemoglobin Glycation Index (HGI = measured A1c − predicted A1c from mean glucose) is roughly normally distributed across the population. "High glycators" sit ~0.5–1.0% above the regression line; "low glycators" sit below it. Red blood cell turnover (mean ~120 days but variable), recent transfusion, iron status, splenectomy, chronic kidney disease, sickle cell trait, thalassemia, and pregnancy all shift A1c away from its expected value given the true mean glucose.

Why CGM TIR is now the preferred metric (ADA 2025)

The ADA Standards of Care 2025 keep A1c < 7% as the headline target for most non-pregnant adults but explicitly elevate Time in Range (TIR, 70–180 mg/dL) > 70% as the primary glycemic target when CGM is available, with Time Below Range (TBR < 70 mg/dL) < 4% and TBR < 54 mg/dL < 1%. The reason is variability: a patient who lives stably at 154 mg/dL and a patient who swings between 70 and 250 mg/dL can both produce a 7.0% A1c and a 154 mg/dL eAG, yet their complication risk profiles diverge sharply — the second patient accumulates hypoglycemia exposure and oxidative-stress spikes that A1c averages out of view. Glycemic Variability metrics — coefficient of variation (CV, target < 36%), Mean Amplitude of Glycemic Excursions (MAGE), standard deviation, and Mean Absolute Relative Difference (MARD) for sensor accuracy — capture what A1c hides.

GMI is replacing eAG in CGM users

The Glucose Management Indicator (GMI), introduced by Bergenstal et al. in Diabetes Care 2018, is calculated directly from CGM mean glucose: GMI (%) = 3.31 + 0.02392 × mean CGM glucose (mg/dL). For people wearing CGM, GMI is preferred to eAG because it is computed from the patient's own sensor data instead of a population regression. A persistent GMI–A1c gap > 0.5% should prompt evaluation for hemoglobinopathy, abnormal RBC lifespan, recent acute glycemic change, or limited CGM wear time.

Pre-meal vs post-meal A1c contribution

Monnier's classic work showed that as overall A1c falls, the contribution of postprandial hyperglycemia rises. At A1c > 10.3% fasting glucose dominates (~70% of the AUC above target). At A1c near 7%, postprandial excursions account for roughly 70% of the burden. Practically: a patient close to target whose A1c is stuck above 7% likely needs prandial intensification (GLP-1 RA, mealtime insulin, or DPP-4i) rather than basal up-titration. eAG alone won't tell you which lever to pull — review the CGM ambulatory glucose profile (AGP) for the answer.

Frequently asked questions

What is my A1c in mg/dL?

Apply the formula eAG (mg/dL) = 28.7 × A1c − 46.7. The most common conversions: A1c 5% = 97 mg/dL, 5.5% = 111, 6% = 126, 6.5% = 140, 7% = 154, 7.5% = 169, 8% = 183, 9% = 212, 10% = 240 mg/dL. Most clinical labs now report eAG automatically alongside the A1c percentage.

What does an A1c of 7% mean in average glucose?

An A1c of 7.0% equals an estimated average glucose of 154 mg/dL (28.7 × 7 − 46.7) over the last 2–3 months. 7% is the standard A1c target the ADA sets for most non-pregnant adults with diabetes, so 154 mg/dL is the everyday glucose level that corresponds to hitting that goal.

What is a normal A1c level?

Per ADA Standards of Care: an A1c below 5.7% is normal (eAG under 117 mg/dL), 5.7–6.4% is prediabetes (eAG 117–137 mg/dL), and 6.5% or higher on two tests meets the diabetes diagnostic threshold (eAG 140 mg/dL and up). The common management target for diagnosed diabetes is below 7% (eAG 154 mg/dL).

What is eAG?

Estimated Average Glucose (eAG) is the mg/dL translation of your HbA1c, calculated as 28.7 × A1c − 46.7 (Nathan, Diabetes Care 2008). The ADA endorsed it so patients could compare lab A1c to the everyday glucometer numbers they're used to seeing.

What is the eAG for an A1c of 6%?

An A1c of 6% corresponds to an eAG of about 126 mg/dL (28.7 × 6 − 46.7 = 125.5). That's right at the diabetes diagnostic threshold for fasting glucose, but the A1c diagnostic cutoff for diabetes is 6.5% — 6.0% sits in the prediabetes range (5.7–6.4%) per ADA Standards of Care.

Why does my CGM average differ from my A1c-derived eAG?

A persistent gap > 0.5% between your CGM 14-day mean glucose and your A1c-derived eAG (or GMI vs A1c) usually points to one of three causes: (1) hemoglobinopathy or abnormal red blood cell turnover — sickle cell trait, thalassemia, hemolytic anemia, recent transfusion, iron deficiency; (2) individual variability in glycation rate (Hemoglobin Glycation Index); or (3) limited CGM wear time biasing the average. Discuss with your endocrinologist.

Is TIR a better metric than A1c?

For patients on CGM, the ADA 2025 Standards of Care now position Time in Range (70–180 mg/dL) > 70% as the primary glycemic target, with A1c as a complementary metric. TIR captures variability and hypoglycemia exposure that A1c averages away. A1c remains the standard when CGM is unavailable and is still the metric tied to long-term complication data from DCCT and UKPDS.

How accurate is eAG for me personally?

The Nathan ADAG regression has a coefficient of variation around 12%, and individual glycation rates vary. About 1 in 4 patients sits more than 10 mg/dL away from the predicted eAG given their true mean glucose. If you're on CGM, GMI from your sensor data is more personalized than eAG from lab A1c.

Why does my daily fingerstick average not match my A1c?

Fingerstick sampling is biased — it tends to be done at predictable times (fasting, pre-meal) and misses postprandial peaks and overnight hypoglycemia. CGM samples every 1–5 minutes and gives a true mean. Even then, glycation rates and red blood cell lifespan vary. A 2–3 week fructosamine can serve as a cross-check when A1c is unreliable.

Should I use GMI or A1c if I wear a CGM?

Use both. GMI (Bergenstal, Diabetes Care 2018: GMI% = 3.31 + 0.02392 × mean CGM glucose mg/dL) reflects the last 14 days from your sensor; A1c reflects ~2–3 months of in-vivo glycation. They answer different questions. The ADA recommends reporting GMI alongside A1c, TIR, TBR, and CV on the standardized Ambulatory Glucose Profile (AGP).

When is fructosamine preferred over A1c?

Fructosamine reflects glycation of serum proteins (mainly albumin) over the past 2–3 weeks. It's preferred when A1c is unreliable: hemoglobinopathies (sickle cell trait, thalassemia), hemolytic anemia, recent transfusion, pregnancy (rapid glycemic changes), end-stage renal disease, or when you need a shorter window after a therapy change.