A1C Calculator

A1C Calculator for Endocrinology. Common anchor points are A1C 6% around 126 mg/dL (7.0 mmol/L), 7% around 154 mg/dL (8.6 mmol/L), 8% around 183 mg/dL (10.1 mmol/L), 9% around 212 mg/dL (11.8 mmol/L), and 10% around 240 mg/dL (13.3 mmol/L). The ADA generally targets A1C below 7% (eAG under 154 mg/dL) for most nonpregnant adults, with a looser goal near 8% for those who are frail, have limited life expectancy, or have a history of severe hypoglycemia, and a tighter goal near 6.5% when it can be achieved without hypoglycemia. If a patient's mean CGM or self-monitored glucose diverges markedly from the eAG, suspect discordance and investigate before adjusting therapy.

How this calculator works

This tool converts a hemoglobin A1C percentage into an estimated average glucose (eAG) using the linear regression derived by Nathan and colleagues in the ADAG study: eAG (mg/dL) = 28.7 × A1C − 46.7, with the SI version eAG (mmol/L) = 1.59 × A1C − 2.59. The relationship is essentially linear across the diabetic range, so each 1% rise in A1C corresponds to roughly 28.7 mg/dL (1.6 mmol/L) higher average glucose. It reflects mean glycemia over the preceding roughly 2 to 3 months, weighted toward the most recent 30 days as older red cells are cleared.

When to use this calculator

Use it to translate a laboratory A1C into an average glucose in the same mg/dL or mmol/L units patients see on their meters or CGM, which makes an abstract percentage actionable during counseling and goal-setting. It applies to established type 1 and type 2 diabetes, where the ADAG equation held across age, sex, race, and diabetes type. Do not rely on eAG when red-cell turnover is abnormal (hemolytic anemia, recent transfusion, iron or B12 deficiency, pregnancy, hemoglobinopathies such as HbSS or HbSC, chronic kidney disease on erythropoietin, or advanced cirrhosis), because A1C then misrepresents true glycemia.

Inputs used

  • Hemoglobin A1C
  • Unit system
  • Clinical context

Clinical interpretation

Common anchor points are A1C 6% around 126 mg/dL (7.0 mmol/L), 7% around 154 mg/dL (8.6 mmol/L), 8% around 183 mg/dL (10.1 mmol/L), 9% around 212 mg/dL (11.8 mmol/L), and 10% around 240 mg/dL (13.3 mmol/L). The ADA generally targets A1C below 7% (eAG under 154 mg/dL) for most nonpregnant adults, with a looser goal near 8% for those who are frail, have limited life expectancy, or have a history of severe hypoglycemia, and a tighter goal near 6.5% when it can be achieved without hypoglycemia. If a patient's mean CGM or self-monitored glucose diverges markedly from the eAG, suspect discordance and investigate before adjusting therapy.

Worked example

A patient with type 2 diabetes has an A1C of 8.0%. eAG = 28.7 × 8.0 − 46.7 = 229.6 − 46.7 = 182.9 mg/dL, or about 183 mg/dL (10.1 mmol/L). This sits well above the ADA general target of below 154 mg/dL (an A1C under 7%), so it signals a need to intensify therapy, and framing it as an average of roughly 183 mg/dL is often more motivating for the patient than the number 8%.

Limitations and safety notes

The ADAG regression carried a roughly 95% confidence band of about plus or minus 15 to 20 mg/dL around any given eAG, so the estimate is a population mean, not a precise individual value, and a person can be a consistent high or low glycator. It was validated only for A1C values roughly between 5% and 12%, and extrapolation beyond that range is unreliable. Because eAG averages highs and lows, a normal-looking value can mask wide glycemic variability and frequent hypoglycemia, which only glucose tracing or time-in-range will reveal. Any condition altering erythrocyte lifespan or hemoglobin structure makes both the A1C and its derived eAG invalid.

Frequently asked questions

Is eAG the same as the average shown on my glucose meter or CGM?

Not exactly. eAG is a statistical estimate derived from A1C, whereas a meter or CGM average is a direct measurement. They usually track closely, but a persistent gap of more than about 15 to 20 mg/dL suggests the patient is an atypical glycator or that a red-cell disorder is affecting the A1C.

Why does the mg/dL formula use 28.7 and −46.7?

Those are the slope and intercept from the linear regression fitted in the ADAG study, which correlated central-lab A1C against roughly 2,700 CGM and fingerstick glucose readings per subject over three months. The SI equivalent is eAG (mmol/L) = 1.59 × A1C − 2.59.

Can I use eAG in pregnancy?

No. Red-cell turnover accelerates in pregnancy, so A1C underestimates true glycemia and the ADAG equation was not validated in pregnant women. Use direct glucose monitoring and pregnancy-specific glycemic targets instead.

Does eAG replace the A1C percentage?

No, it complements it. Guideline targets and cardiovascular-risk data are anchored to the A1C percentage, so report both: the percentage for clinical decisions and the eAG to help patients relate the result to the numbers they see every day.

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. PMID: 18540046.
  • American Diabetes Association Professional Practice Committee. 6. Glycemic Goals and Hypoglycemia: Standards of Care in Diabetes—2024. 2024.

Editorial review and citation methodology

Reviewed by the Quick Medical Calculator Editorial Team. Last reviewed: May 17, 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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