HbA1c Calculator
HbA1c is the most important blood test for monitoring long-term blood glucose control in people with diabetes, and for screening and diagnosing the condition. It reflects average blood glucose over the past 2-3 months. Results are reported in two units: NGSP percentage (%) used in the US and some other countries, and IFCC mmol/mol used internationally. This calculator converts between the two units, computes estimated average glucose (eAG) in both mg/dL and mmol/L, and classifies your HbA1c against ADA diagnostic thresholds. Enter your result in either unit and the calculator provides the conversion and clinical context.
HbA1c conversion formulas (IFCC/NGSP)
IFCC (mmol/mol) = (NGSP % - 2.15) x 10.929
NGSP % = (IFCC mmol/mol / 10.929) + 2.15
eAG (mg/dL) = 28.7 x NGSP % - 46.7
eAG (mmol/L) = eAG (mg/dL) / 18.018
HbA1c: frequently asked questions
What is HbA1c?
HbA1c (glycated haemoglobin) reflects your average blood glucose over the past 2-3 months. When glucose attaches to haemoglobin in red blood cells, it forms HbA1c. Because red blood cells live about 90 days, HbA1c provides a picture of long-term blood sugar control. It is the primary test for diagnosing and monitoring diabetes.
What is a normal HbA1c level?
Per the American Diabetes Association: below 5.7% (39 mmol/mol) is normal; 5.7-6.4% (39-46) is prediabetes; 6.5% (48 mmol/mol) or above is diabetes. For people with diabetes, the ADA recommends an HbA1c below 7% (53 mmol/mol) for most patients, though targets are individualised.
What is the difference between NGSP % and IFCC mmol/mol?
NGSP % (US units) and IFCC mmol/mol are two standards for reporting HbA1c. The US and many other countries use %, while Europe and some other regions use mmol/mol. The conversion formula is: IFCC (mmol/mol) = (NGSP % - 2.15) x 10.929.
What is estimated average glucose (eAG)?
eAG estimates the average blood glucose level corresponding to an HbA1c result, in mg/dL or mmol/L. The ADA formula is: eAG (mg/dL) = 28.7 x HbA1c (%) - 46.7. This helps patients relate lab HbA1c results to the glucose numbers they see on their home meter.
What factors can falsely affect HbA1c?
HbA1c can be falsely high in iron deficiency anaemia, kidney disease, and certain haemoglobin variants. It can be falsely low in haemolytic anaemia, sickle cell trait, and after blood transfusions. In these situations, alternative methods such as fructosamine may be used to assess glycaemic control.
Official sources
- American Diabetes Association: Diagnosis of Diabetes.
- National Institute of Diabetes and Digestive and Kidney Diseases: A1C Test and Diabetes.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.