Estimated Average Glucose (eAG) Calculator

Estimated Average Glucose (eAG) Calculator for Endocrinology. Anchor points worth memorizing: A1c 6% approximately 126 mg/dL, 7% approximately 154 mg/dL, 8% approximately 183 mg/dL, 9% approximately 212 mg/dL, 10% approximately 240 mg/dL. When a patient's measured mean glucose sits well above their eAG, suspect a "high glycator" phenotype, post-meal spikes their fingersticks miss, or shortened red-cell survival; when it sits well below, suspect frequent unrecorded hypoglycemia or a low-glycator phenotype. The eAG does not replace the A1c target itself - most nonpregnant adults still aim for A1c under 7% (eAG under 154 mg/dL), individualized by hypoglycemia risk and comorbidity.

How this calculator works

This tool converts a laboratory HbA1c into an estimated average glucose using the linear regression derived by the A1C-Derived Average Glucose (ADAG) study: eAG (mg/dL) = 28.7 x A1c - 46.7, or equivalently eAG (mmol/L) = 1.59 x A1c - 2.59. The regression was fit against roughly 2,700 glucose readings per subject over 3 months, combining continuous glucose monitoring with seven-point self-monitoring, and explained 84% of the variance in mean glucose (R-squared 0.84). It is a deterministic transformation, not a measurement, so it inherits both the precision and the biological caveats of the HbA1c it is built from.

When to use this calculator

Use eAG to translate a periodic HbA1c into the mg/dL or mmol/L units patients see on their meters and CGM, making an abstract percentage tangible during counseling on type 1 or type 2 diabetes. It is most useful when a patient's day-to-day glucose readings and their HbA1c seem to disagree, prompting a search for causes. Do not use eAG in conditions that decouple HbA1c from true glycemia: hemoglobinopathies, recent transfusion or hemolysis, iron-deficiency or B12-deficiency anemia, pregnancy, advanced CKD/dialysis, or erythropoietin therapy.

Inputs used

  • Hemoglobin A1C

Clinical interpretation

Anchor points worth memorizing: A1c 6% approximately 126 mg/dL, 7% approximately 154 mg/dL, 8% approximately 183 mg/dL, 9% approximately 212 mg/dL, 10% approximately 240 mg/dL. When a patient's measured mean glucose sits well above their eAG, suspect a "high glycator" phenotype, post-meal spikes their fingersticks miss, or shortened red-cell survival; when it sits well below, suspect frequent unrecorded hypoglycemia or a low-glycator phenotype. The eAG does not replace the A1c target itself - most nonpregnant adults still aim for A1c under 7% (eAG under 154 mg/dL), individualized by hypoglycemia risk and comorbidity.

Worked example

A patient with an HbA1c of 7.0% gives eAG = 28.7 x 7.0 - 46.7 = 154 mg/dL (8.6 mmol/L). An HbA1c of 8.0% yields 183 mg/dL (10.2 mmol/L), and 6.0% yields 126 mg/dL (7.0 mmol/L) - so each 1% rise in A1c corresponds to roughly 29 mg/dL of average glucose. A patient whose meter averages near 190 mg/dL but whose lab A1c is 7.0% (eAG 154) has a real discrepancy worth investigating.

Limitations and safety notes

The 95% confidence interval around eAG is wide: an A1c of 7.0% corresponds to a true mean glucose plausibly spanning roughly 123-185 mg/dL, so eAG is a point estimate, not a precise value. The ADAG cohort was 89% white and excluded children, pregnant women, and people with significant anemia or kidney disease, so extrapolation to those groups is unvalidated. Because it is derived from mean glucose, eAG says nothing about glycemic variability or time in hypoglycemia, and two patients with identical eAG can have very different glucose profiles.

Frequently asked questions

Why does my patient's meter average not match the eAG?

Meters sample only a few points per day and often miss overnight and post-meal excursions, whereas eAG reflects a continuous 3-month mean. Persistent divergence can also reflect inter-individual differences in glycation rate or altered red-cell lifespan.

Is eAG the same as the 'GMI' from a CGM report?

No. eAG is derived from a lab HbA1c using the ADAG equation, while the Glucose Management Indicator (GMI) is calculated directly from CGM sensor glucose over 14 or more days. They use different formulas and can differ by 0.5% or more; do not treat them as interchangeable.

Can I use eAG to diagnose diabetes?

No. Diagnosis rests on the HbA1c value itself (6.5% threshold) or on fasting/OGTT/random plasma glucose. eAG is a communication and interpretation aid, not a diagnostic cutoff.

Does the formula change for mmol/L?

The same regression is simply rescaled: eAG (mmol/L) = 1.59 x A1c - 2.59. This gives the average glucose in the SI units used across most of the world outside the United States.

References

  • Nathan DM, Kuenen J, Borg R, Zheng H, Schoenfeld D, Heine RJ; A1c-Derived Average Glucose (ADAG) Study Group. Translating the A1C assay into estimated average glucose values. Diabetes Care. 2008;31(8):1473-8. PMID: 18540046.
  • American Diabetes Association Professional Practice Committee. 6. Glycemic Goals and Hypoglycemia: Standards of Care in Diabetes-2024. Diabetes Care. 2024;47(Suppl 1):S111-S125. doi:10.2337/dc24-S006.

Editorial review and citation methodology

Reviewed by the Quick Medical Calculator Editorial Team. Last reviewed: May 18, 2026. The review checks calculator inputs, intended population, interpretation, limitations, and source alignment.

  • Prefer original validation studies for scoring systems and prediction tools.
  • Use current specialty society guidance, transplant allocation policy, public health guidance, or regulator resources when they govern clinical use.
  • Include limitations and safety notes when a calculator is population-specific, context-dependent, or unsuitable as a standalone decision tool.

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