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Glucose to A1c Calculator

Estimate A1c from average glucose.

Result

7.0%

How it is calculated

The tool estimates HbA1c, the percentage of haemoglobin carrying glucose, from the average blood glucose in mg/dL using the linear relationship HbA1c (%) = (average glucose + 46.7) / 28.7. This is the reverse of the common conversion eAG = 28.7 × A1C - 46.7. Glucose must be above zero and is not range-checked, so unrealistic values still produce a number. The result is rounded to one decimal. HbA1c reflects roughly the previous two to three months, so a short run of readings may not match a lab result. It is an estimate, not a diagnosis, and individuals can differ from the average relationship.

Worked example

An average blood glucose of 154 mg/dL. Add the constant: 154 + 46.7 = 200.7. Divide by 28.7: 200.7 / 28.7 = 6.99. Rounded to one decimal, the estimated HbA1c is 7.0%. Going the other way, an HbA1c of 7% corresponds to an average glucose of 28.7 × 7 - 46.7 = 154.2 mg/dL.

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Common mistakes

  • Entering glucose in mmol/L. The formula expects mg/dL; multiply mmol/L by about 18 first.
  • Using a single fasting reading as the average. The relationship is for the average over weeks.
  • Comparing the estimate with a lab HbA1c and assuming one must be wrong. Conditions such as anaemia can shift the lab value.
  • Confusing HbA1c percent with the newer mmol/mol unit.

About this calculator

This calculator estimates HbA1c from an average blood glucose reading, using the reverse of the ADAG study formula (A1c = (eAG + 46.7) / 28.7), the same equation labs use in the opposite direction to translate a meter's average glucose into the A1c percentage doctors track over three months.

Diabetes educators and patients use it to get a rough sense of where their A1c might land based on their glucose meter's average, and nursing and medical students use it to practice the eAG-to-A1c relationship. It's an estimate for education purposes, not a substitute for a lab-drawn A1c test.

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