HbA1c Calculator (A1c to eAG)

HbA1c measures the proportion of hemoglobin that is glycated. It indirectly reflects average glycemia over roughly the prior 2–3 months, with recent weeks contributing more heavily, but it does not show individual glucose excursions or hypoglycemia.

The 2008 ADAG regression translates NGSP HbA1c to eAG: eAG in mg/dL equals 28.7 times A1C minus 46.7, and eAG in mmol/L equals 1.5944 times A1C minus 2.594. eAG is a study-derived estimate, not a directly measured average.

No. eAG is a population regression estimate. An individual’s measured mean glucose, CGM mean glucose or glucose management indicator may differ, and eAG does not show time in range, variability, post-meal peaks or hypoglycemia.

IFCC mmol/mol equals 10.93 times NGSP percent minus 23.50. NGSP percent equals 0.09148 times IFCC mmol/mol plus 2.152. The calculator retains unrounded intermediate values.

For appropriate nonpregnant diagnostic contexts, below 5.7% or 39 mmol/mol is below the prediabetes threshold, 5.7–6.4% or 39–47 mmol/mol is the prediabetes range, and at least 6.5% or 48 mmol/mol is the diabetes threshold. An NGSP-certified, DCCT-traceable laboratory method is required.

Not generally. In the absence of unequivocal hyperglycemia, diagnosis requires confirmatory testing with an appropriate laboratory method. This calculator provides threshold context and cannot establish a diagnosis.

A1C cannot determine diabetes type and should not be used alone to diagnose gestational diabetes. Symptoms, pregnancy-specific testing, plasma glucose and the full clinical context are required.

ADA 2026 describes below 7% as a general goal for many nonpregnant adults with diabetes, not a universal target. Goals are individualized for hypoglycemia risk, age, functional status, comorbidities, life expectancy, treatment burden and personal priorities; this page does not recommend medication changes.

For people with stable glycemia who are meeting goals, A1C is commonly measured about twice yearly. When goals are not met, treatment changes or glycemia is unstable, assessment about every 3 months is commonly appropriate, subject to the clinical plan.

Altered red-cell survival or production can make A1C falsely high or low. Examples include hemolytic or iron-deficiency anemia, recent blood loss, transfusion, kidney failure, dialysis, pregnancy, erythropoietin therapy, G6PD deficiency, HIV and liver disease. Direction and magnitude depend on the mechanism and assay.

Hemoglobin variants can cause method-dependent analytic interference or change red-cell survival. HbSS, HbCC, HbSC and other conditions without normal HbA require particular caution. The laboratory method and NGSP interference information should be reviewed.

Investigate red-cell or assay interference, the laboratory method and hemoglobin variants. Plasma-glucose criteria may be used for diagnosis, while BGM, CGM, fructosamine or glycated albumin may be considered for monitoring in an appropriate clinical context. This page does not select a test or treatment.