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HbA1c to Average Glucose Calculator

Convert an HbA1c result to estimated average glucose (eAG) and IFCC units.

Everyone & professionalsDiabetes & metabolic healthv1.1.0

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Enter your measurements, then press Calculate.

Methodology

ADAG regression (Nathan et al., 2008)

eAG (mg/dL) = 28.7 × HbA1c (%) − 46.7; IFCC (mmol/mol) = (NGSP − 2.152) ÷ 0.09148

The A1c-Derived Average Glucose study related HbA1c to average glucose measured by continuous monitoring over three months.

Who it is for
Adults with or without diabetes; HbA1c between 4% and 15%.
Version
1.1.0

How this calculator works

Where the formula comes from

  • The A1c-Derived Average Glucose (ADAG) study of 507 adults (268 with type 1 diabetes, 159 with type 2, 80 without diabetes) in 10 international centres produced the equation eAG (mg/dL) = 28.7 × HbA1c − 46.7.[1]
  • Average glucose was measured with continuous glucose monitoring plus fingerstick readings over about three months; the regression explained 84% of the variation (R² = 0.84).[1]
  • The ADAG analysis did not find statistically significant differences in the HbA1c–average glucose relationship by age, sex, diabetes type, race/ethnicity or smoking.[1]

The inputs

  • HbA1c is entered as an NGSP percentage; NGSP % and IFCC mmol/mol are linked by a standard master equation.[1]

Versions and alternatives

  • An earlier regression from the DCCT data gave mean plasma glucose (mg/dL) = 35.6 × HbA1c − 77.3.[2]
  • The Glucose Management Indicator works the other way, estimating HbA1c from mean glucose measured by continuous monitoring.[3]

Where accuracy falls (published evidence)

  • The equation describes a population relationship; the same HbA1c can correspond to a range of average glucose values in different people.[1]
  • In pregnancy the relationship between HbA1c and average glucose may differ, so the standard ADAG equation should not be assumed to be accurate.[4]
  • HbA1c may be misleading when red-cell turnover or haemoglobin-related factors alter its relationship with glucose, for example in some anaemias, haemoglobin variants and some kidney-related conditions.[5]

What guidelines say

  • The American Diabetes Association recommends investigating marked discordance between HbA1c and measured glucose levels.[5]

Sources

  1. Nathan DM, Kuenen J, Borg R, Zheng H, Schoenfeld D, Heine RJ; ADAG Study Group. Translating the A1C assay into estimated average glucose values. Diabetes Care. 2008;31(8):1473–1478. doi:10.2337/dc08-0545
  2. Rohlfing CL, Wiedmeyer HM, Little RR, England JD, Tennill A, Goldstein DE. Defining the relationship between plasma glucose and HbA1c: analysis of glucose profiles and HbA1c in the Diabetes Control and Complications Trial. Diabetes Care. 2002;25(2):275–278. doi:10.2337/diacare.25.2.275
  3. Bergenstal RM, Beck RW, Close KL, et al. Glucose Management Indicator (GMI): a new term for estimating A1C from continuous glucose monitoring. Diabetes Care. 2018;41(11):2275–2280. doi:10.2337/dc18-1581
  4. Law GR, Gilthorpe MS, Secher AL, et al. Translating HbA1c measurements into estimated average glucose values in pregnant women with diabetes. Diabetologia. 2017;60(4):618–624. doi:10.1007/s00125-017-4205-7
  5. American Diabetes Association Professional Practice Committee. 2. Diagnosis and classification of diabetes: Standards of Care in Diabetes—2025. Diabetes Care. 2025;48(Suppl 1):S27–S49. doi:10.2337/dc25-S002

Compiled from the published sources above. Every statement was agreed independently by three AI research tools (Claude, ChatGPT, DeepSeek) and its source verified in PubMed or Crossref by the Hakeemly editorial team. Not reviewed by a doctor unless stated. Agreed on

Worked example: how to calculate hbA1c → average glucose

Inputs

HbA1c
7 % (NGSP)

Result

Estimated average glucose
154 mg/dL
Estimated average glucose
8.6 mmol/L
HbA1c (IFCC)
53 mmol/mol
HbA1c (NGSP)
7 %

Calculation:

28.7×7−46.7 = 154.2; (7−2.152)÷0.09148 = 53.0

An illustration with sample values, worked out with the same method the tool above uses.

Limitations

  • Anaemia, haemoglobin variants, kidney disease and pregnancy can make HbA1c misleading.
  • The same HbA1c can reflect a range of average glucose values.

References

  1. Nathan DM, Kuenen J, Borg R, Zheng H, Schoenfeld D, Heine RJ; ADAG Study Group. Translating the A1C assay into estimated average glucose values. Diabetes Care. 2008;31(8):1473–1478. doi:10.2337/dc08-0545
  2. American Diabetes Association Professional Practice Committee. 2. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes—2025. Diabetes Care. 2025;48(Suppl 1):S27–S49. doi:10.2337/dc25-S002

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