HbA1c to Average Glucose Calculator
Convert your HbA1c percentage into an estimated average blood glucose (eAG).
What this calculator does
HbA1c is reported as a percentage, but most people are more used to thinking about blood sugar in mg/dL (or mmol/L). This tool converts your HbA1c into an estimated average glucose (eAG) - the average blood sugar level your HbA1c reflects over roughly the last three months.
How it works
It uses the ADAG study formula, eAG (mg/dL) = 28.7 x HbA1c - 46.7, and also shows the mmol/L equivalent. HbA1c measures how much sugar has attached to your red blood cells, which turn over about every three months, so it captures a longer-term trend than a single glucose test. Everything is calculated in your browser and nothing is stored.
What your result means
| HbA1c | Category | Estimated average glucose |
|---|---|---|
| Below 5.7% | Normal | Below about 117 mg/dL |
| 5.7 to 6.4% | Prediabetes | About 117 to 137 mg/dL |
| 6.5% and above | Diabetes | About 140 mg/dL and above |
A diagnosis of diabetes is not made on one reading. It needs a repeat test or a second abnormal result, and your doctor will interpret it alongside symptoms and other tests.
Things to keep in mind
eAG is an estimate of an average, so it will not match any single glucometer reading. HbA1c can also be misleading when red blood cells do not survive a normal three months - for example in anaemia, after recent blood loss, with some inherited haemoglobin variants, or during pregnancy. In those cases a fasting or post-meal glucose test, or a continuous glucose monitor, may reflect your control better. Always review your numbers with your doctor before changing anything.
Frequently asked questions
What is estimated average glucose (eAG)?
eAG translates your HbA1c into the same units as a glucose test (mg/dL or mmol/L). It represents your average blood sugar over roughly the previous three months.
Why does my eAG not match my glucometer reading?
eAG is a three-month average. A finger-prick reading is a single moment that rises after meals and falls with fasting, so individual readings will be above or below the average.
What HbA1c counts as normal, prediabetes or diabetes?
Below 5.7% is normal, 5.7 to 6.4% is the prediabetes range, and 6.5% or above (confirmed on a repeat test) meets the threshold for diabetes.
Can HbA1c be falsely high or low?
Yes. Anaemia, recent blood loss or transfusion, certain haemoglobin variants, and pregnancy can all make HbA1c misleading. Your doctor may use a glucose test instead in those situations.
How often should HbA1c be checked?
For most people with diabetes it is checked every three to six months. Ask your doctor what interval is right for you.
Formula source: Nathan DM et al. Translating the A1C assay into estimated average glucose values. Diabetes Care 2008;31:1473-1478.
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