HbA1c to average glucose (eAG) converter

What glycated hemoglobin shows

HbA1c is the share of hemoglobin bound to glucose. Because red blood cells live about 3 months, HbA1c reflects your average sugar over the past 2–3 months and doesn’t depend on whether you ate before the test. That’s why it’s used both to diagnose diabetes and to monitor treatment.

Normal is below 5.7%. The 5.7–6.4% range is prediabetes (a reason to review diet and weight); 6.5% and above on repeat tests is a diabetes criterion.

How HbA1c converts to average glucose (eAG)

HbA1c percentages are hard to relate to familiar meter numbers. The ADAG formula (Nathan, 2008) converts HbA1c into estimated average glucose (eAG): eAG (mg/dL) = 28.7 × HbA1c − 46.7, then converted to mmol / L. For example, HbA1c 6.0% ≈ 7.0 mmol / L, 7.0% ≈ 8.6 mmol / L, 8.0% ≈ 10.2 mmol / L.

eAG is an average, not a fasting value: it blends morning and post-meal levels across the quarter, so it’s usually higher than the “morning” fasting glucose on a report.

Why it’s useful

Average glucose in mmol / L helps you see how far your daily meter numbers sit from the norm on average, and gauge the effect of changes to diet and treatment. A single HbA1c isn’t the full picture: it’s read together with fasting glucose, and — for insulin-resistance questions — with the HOMA-IR index.