HbA1c to eAG Calculator — Convert HbA1c % or mmol/mol to Average Glucose

Convert HbA1c to estimated average glucose (eAG) — instantly, in either direction. Enter any of the four values below and the others update automatically. The conversion uses the formula validated by the ADAG (A1c-Derived Average Glucose) study, the same equation used by the American Diabetes Association.

How the conversion works

HbA1c reflects your average blood glucose over roughly the previous 8–12 weeks (the lifespan of a red blood cell). The estimated average glucose (eAG) is that same average expressed in the units you’d see on a finger-prick or CGM — making the number easier to relate to day-to-day readings.

Two formulas are used here:

• HbA1c% to eAG mg/dL: eAG = 28.7 × HbA1c − 46.7 — derived from the ADAG study (Nathan et al., Diabetes Care 2008), used by the ADA.
• HbA1c% (DCCT) to mmol/mol (IFCC): mmol/mol = (HbA1c% − 2.152) / 0.09148 — the master equation used by the NGSP, NICE, and the IFCC.
• mg/dL to mmol/L: divide by 18.018.

Reference ranges

What HbA1c does not tell you

• Time in range. Two people with HbA1c 7.0% (53 mmol/mol) can have completely different glucose patterns. CGM data is needed to see this.
• Hypoglycaemia. HbA1c can look “good” because frequent lows are pulling the average down — a dangerous picture.
• Recent changes. A diet or medication change in the past 2–3 weeks may not be fully reflected yet.
• Conditions that distort HbA1c — pregnancy, anaemia, recent blood transfusion, haemoglobinopathies, chronic kidney disease, and some medications can all shift HbA1c away from what your true average glucose has been. Your team will know whether this applies to you.

Frequently asked questions

What’s the difference between HbA1c % and HbA1c mmol/mol?

They’re the same measurement on two scales. The “%” (DCCT/NGSP) scale is older and more familiar in the US. The mmol/mol (IFCC) scale was internationally standardised and is the primary unit reported in the UK and most of Europe. Conversion is direct and exact.

Is eAG the same as my CGM average?

Close, but not identical. The eAG formula was derived from a mix of capillary, venous, and CGM data. Your CGM average (often called GMI — Glucose Management Indicator) is calculated from CGM data alone and may differ by up to 0.5% from your laboratory HbA1c. If they disagree, the lab HbA1c is usually the trusted value, but a persistent gap is worth discussing with your team.

What HbA1c should I aim for?

NICE NG28 recommends an individualised target — typically 48 mmol/mol (6.5%) for adults managed by diet or a single non-hypoglycaemic medication, and 53 mmol/mol (7.0%) for those on a medication carrying hypoglycaemia risk. Older adults, those with frailty, or those with recurrent hypoglycaemia have higher targets. Discuss your personal target with your diabetes team.

How often should HbA1c be checked?

Every 3–6 months until stable, then 6–12 monthly under NICE NG28 — and any time treatment changes substantially.

Can HbA1c be falsely low or high?

Yes. Conditions that shorten red-cell lifespan (haemolysis, recent transfusion, certain anaemias) can falsely lower HbA1c. Iron-deficiency anaemia, vitamin B12 deficiency, splenectomy, and some haemoglobin variants can falsely raise it. In all of these cases, fructosamine or CGM-derived GMI may be a better marker.

Related guides

• Type 2 Diabetes: Symptoms, Diagnosis, and Management
• Diabetes Medications: a complete guide
• Diabetes Complications: Heart, Kidney, Eye, and Foot Health

References: Nathan DM et al. Translating the A1C assay into estimated average glucose values. Diabetes Care 2008;31:1473-78. NGSP master equation. NICE NG28 (Type 2 diabetes in adults). ADA Standards of Care 2026.

Reviewed: May 2026.