A1C to eAG Calculator

HbA1c and average glucose measure the same underlying thing from two directions. A single finger-prick reading is a snapshot of blood sugar at that moment. HbA1c, by contrast, reflects the glucose that has been attaching to haemoglobin in your red blood cells over the previous two to three months, which is roughly how long those cells live. That is why it is used both for diagnosing diabetes and for judging how well control is going over the medium term.

Converting between them became standard after the ADAG study, which fitted a straight line through thousands of paired A1C tests and continuous glucose monitor readings. The relationship is estimated average glucose in mg/dL equals 28.7 times the A1C percentage minus 46.7. An A1C of 6.5 per cent, the conventional diagnostic threshold for diabetes, corresponds to an average glucose of about 140 mg/dL, or roughly 7.8 mmol/L. An A1C of 7 per cent is about 154 mg/dL and 8 per cent about 183 mg/dL.

Understanding the average is useful because it reframes what control means. An average of 140 mg/dL can come from remarkably steady readings, or from a mix of frequent highs and lows, and those two patterns are very different experiences. Two people with identical A1C levels can have quite different daily lives. This is one reason continuous glucose monitoring, which reveals the time spent in range, has become so important alongside HbA1c.

Several limits are worth knowing. The formula assumes a normal red blood cell lifespan, so anaemia, recent blood loss, some haemoglobin variants, pregnancy and chronic kidney disease can all make A1C misleading — in those situations A1C may not reflect true glucose levels, and clinicians use other measures. A1C also cannot be used to diagnose diabetes in people with certain conditions, and it changes slowly, so it is a poor tool for judging a single day's decisions. Most importantly, this is an educational conversion, not a diagnosis or a treatment target. Whether your values are acceptable, and what to do about them, depends on your history, medications and other conditions — take the numbers to your doctor or diabetes team rather than acting on them yourself.

This calculator returns estimates for general information only. It is not medical advice, diagnosis or treatment, and it cannot replace an assessment by a qualified health professional. Individual results vary, and figures such as calorie needs, body-fat percentage and heart-rate zones are approximations based on population averages rather than measurements of you.