Translates HbA1c into the glucose number you see on a meter.
What does HbA1c mean?
HbA1c (glycated haemoglobin, or haemoglobin A1c) is a blood test that measures what percentage of your haemoglobin, the oxygen-carrying protein in red blood cells, has glucose attached to it. Because red blood cells circulate for approximately 90–120 days before being replaced, the HbA1c level reflects your average blood glucose over the preceding 2–3 months, making it a much more reliable indicator of long-term glucose control than a single fasting glucose measurement.
This calculator uses the ADAG (A1C-Derived Average Glucose) equation published by Nathan and colleagues in Diabetes Care in 2008, derived from the international ADAG study in which continuous glucose monitoring and HbA1c measurements were correlated in 507 adults with and without diabetes. The equation is: eAG (mmol/L) = 1.59 × HbA1c(%) − 2.59.
The estimated average glucose (eAG) produced by this calculator represents the same type of glucose measurement shown on home glucose meters and continuous glucose monitors, expressed in either mmol/L (SI) or mg/dL (US units). This helps patients understand what their HbA1c means in everyday terms.
HbA1c is used both for diagnosing diabetes and prediabetes, and for monitoring glycaemic control in people with diabetes. Most major diabetes organisations recommend an HbA1c target below 7.0% (53 mmol/mol) for most adults with type 2 diabetes, though personalised targets account for age, hypoglycaemia risk, and comorbidities.
Reference ranges
| Category | HbA1c (%) | eAG (mmol/L) |
|---|---|---|
| Normal | < 5.7 | < 7.0 |
| Prediabetes | 5.7 – 6.4 | 7.0 – 9.0 |
| Diabetes diagnosis | ≥ 6.5 | ≥ 9.0 |
| Target (most adults with T2DM) | < 7.0 | < 10.2 |
| High / poor control | > 9.0 | > 14.6 |
When should you see a doctor?
An HbA1c of 5.7% or above warrants discussion with a doctor, even if you feel well. Prediabetes (5.7–6.4%) is reversible with lifestyle intervention, and early action substantially reduces the risk of progressing to type 2 diabetes. An HbA1c of 6.5% or above meets the diagnostic threshold for diabetes and requires formal clinical management. Any individual with a history of gestational diabetes, cardiovascular disease, or strong family history of type 2 diabetes should have their HbA1c checked regularly.