What is eAG (estimated average glucose) and how is it calculated?

eAG (estimated average glucose) translates your HbA1c result into the same units — mg/dL or mmol/L — that appear on a home glucose meter, making it easier to understand what your A1c means day-to-day. The formula is derived from the ADAG study (Nathan et al., Diabetes Care 2008), which used continuous glucose monitoring and frequent point glucose measurements in 507 people across 10 international centres. The equations are: eAG (mg/dL) = 28.7 × HbA1c% − 46.7, and eAG (mmol/L) = 1.59 × HbA1c% − 2.59. Because these are population averages, your personal eAG may differ by ±15–20 mg/dL due to individual variation in glycation rates and red cell lifespan.

What are the target HbA1c levels for people with diabetes?

For most non-pregnant adults with type 1 or type 2 diabetes, the ADA recommends an HbA1c target of less than 7.0% (53 mmol/mol). Less stringent targets (e.g., less than 8.0% / 64 mmol/mol) may be appropriate for older adults, people with a history of severe hypoglycaemia, limited life expectancy, or multiple comorbidities. More stringent targets (less than 6.5% / 48 mmol/mol) can be considered for younger individuals with short disease duration if achievable without significant hypoglycaemia. Targets for women with pre-existing diabetes during pregnancy are typically 6.0–6.5% (42–48 mmol/mol). Always individualise targets in discussion with your healthcare team.

HbA1c to Average Glucose Converter

Convert between HbA1c % (NGSP), HbA1c mmol/mol (IFCC), and estimated average glucose (eAG) in mg/dL or mmol/L. Type any value — all four update instantly. ADA diagnostic categories shown automatically.

HbA1c

HbA1c — NGSP %

HbA1c — IFCC mmol/mol

mmol/mol

Estimated Average Glucose (eAG)

eAG — mg/dL

mg/dL

eAG — mmol/L

mmol/L

HbA1c (NGSP)

--%

HbA1c (IFCC)

--mmol/mol

eAG

--mg/dL

eAG

--mmol/L

Normal
<5.7% Prediabetes
5.7–6.4% Diabetes
6.5–7.9% Diabetes
8.0%+

What HbA1c Measures

Haemoglobin A1c (HbA1c) is the fraction of haemoglobin in your red blood cells that has become glycated — permanently bound to glucose through a non-enzymatic reaction. The higher your average blood glucose over the previous 8–12 weeks, the more glucose attaches to haemoglobin, and the higher your HbA1c climbs. Because red blood cells live for roughly 90 to 120 days, a single HbA1c result reflects a weighted average of the last two to three months of glycaemic control, with the most recent weeks contributing the most.

The American Diabetes Association (ADA) and the International Diabetes Federation (IDF) both endorse HbA1c as a diagnostic criterion for prediabetes and type 2 diabetes. It has several practical advantages over fasting glucose: it does not require fasting, is less susceptible to day-to-day variation, and provides a time-averaged picture that better reflects chronic glucose exposure. The eAG value produced by this converter translates your HbA1c into the everyday units shown on a home glucose meter, helping bridge the gap between your lab report and your daily readings.

Diabetes Diagnostic Categories

The table below shows ADA diagnostic thresholds. Note that a single abnormal result should typically be confirmed on a second occasion before a clinical diagnosis is made.

Category	HbA1c %	HbA1c mmol/mol	eAG mg/dL	eAG mmol/L
Normal	<5.7%	<39 mmol/mol	<117 mg/dL	<6.5 mmol/L
Prediabetes	5.7–6.4%	39–47 mmol/mol	117–137 mg/dL	6.5–7.6 mmol/L
Diabetes	≥6.5%	≥48 mmol/mol	≥140 mg/dL	≥7.8 mmol/L
Diabetes target (most adults)	<7.0%	<53 mmol/mol	<154 mg/dL	<8.6 mmol/L

NGSP vs IFCC: Why There Are Two HbA1c Numbers

If you have ever compared a UK lab report with a US one, you may have noticed a curious difference: the US report says something like "HbA1c: 7.0%" while the UK report says "HbA1c: 53 mmol/mol." These are two different standardisation systems for measuring the same molecule. The NGSP (National Glycohemoglobin Standardization Program) was built around the landmark DCCT and UKPDS clinical trials of the 1980s and 1990s, which expressed HbA1c as a percentage of total haemoglobin using a specific chromatographic reference method. The IFCC (International Federation of Clinical Chemistry and Laboratory Medicine) later developed a more chemically precise reference method that measures only the specific glycated N-terminal peptide of the haemoglobin beta chain, expressing results in millimoles of glycated haemoglobin per mole of total haemoglobin. The IFCC scale produces numerically lower values — 53 mmol/mol corresponds to 7.0% NGSP — and the UK switched to IFCC reporting in 2011. The conversion formula used by this tool is: IFCC (mmol/mol) = (NGSP% − 2.15) × 10.929, as defined by the IFCC-NGSP network consensus.

Limitations of HbA1c

HbA1c is a highly useful marker, but it is not reliable in every clinical situation. Results can be significantly altered by conditions that affect red blood cell production, lifespan, or haemoglobin structure:

Haemoglobinopathies (sickle cell disease, thalassaemia, HbC, HbE, HbD). Abnormal haemoglobin variants can interfere with some HbA1c assay methods, producing falsely low or falsely high results depending on the method used. Genetic testing and fructosamine or glycated albumin should be considered in these patients.
Iron deficiency anaemia. Iron deficiency can prolong red blood cell lifespan, causing glucose to accumulate on haemoglobin for longer and leading to falsely elevated HbA1c values — sometimes by 0.5–1.0 percentage points above true glycaemic levels.
Recent blood transfusion. Transfused red blood cells from a donor who may have different glucose exposure will dilute the patient's HbA1c, producing spuriously low values for 1–3 months after transfusion.
Haemolytic anaemia, chronic kidney disease (CKD), and erythropoietin therapy. Conditions that accelerate red blood cell destruction or stimulate new red blood cell production shorten the average cell lifespan, leading to falsely low HbA1c because cells have had less time to accumulate glucose.
Pregnancy. Increased red blood cell turnover during pregnancy, particularly in the second and third trimesters, shortens average red cell lifespan and lowers HbA1c independently of glucose levels. Gestational diabetes screening and management typically relies on glucose tolerance tests rather than HbA1c alone.
CGM-derived GMI vs. laboratory HbA1c. The Glucose Management Indicator (GMI) calculated from continuous glucose monitor (CGM) data uses a different formula (GMI% = 3.31 + 0.02392 × mean glucose in mg/dL) derived from a separate cohort study. GMI and laboratory HbA1c frequently differ by 0.5% or more in the same individual because CGM captures glucose over 3 months but cannot account for the biology of red cell lifespan and glycation variability that affects HbA1c. Neither is simply "more accurate" — they measure related but distinct phenomena.

In any of the above situations, fasting plasma glucose, 2-hour oral glucose tolerance testing, or continuous glucose monitoring may provide more accurate information about glycaemic status.

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Frequently Asked Questions

What is HbA1c and what does it measure?

HbA1c (glycated haemoglobin, also called A1c or glycohaemoglobin) measures the fraction of haemoglobin molecules in your red blood cells that have glucose permanently attached to them. Because red blood cells live for roughly 2–3 months, your HbA1c reflects your average blood glucose over that time. The ADA and IDF use it as a primary diagnostic criterion for prediabetes and diabetes. An HbA1c of 7.0% (53 mmol/mol) corresponds to an estimated average glucose of approximately 154 mg/dL (8.6 mmol/L).

How is HbA1c different from a fasting glucose test?

A fasting plasma glucose test measures how much glucose is in your blood after an 8-hour fast — it is a snapshot of one moment in time. HbA1c integrates your glucose exposure over the full 8–12-week red blood cell lifespan. HbA1c does not require fasting and is less affected by day-to-day variation in diet or stress. However, certain conditions (haemoglobinopathies, anaemia, CKD) can make HbA1c unreliable, and in those cases fasting glucose or a glucose tolerance test is preferred.

What is the difference between NGSP (%) and IFCC (mmol/mol)?

NGSP expresses HbA1c as a percentage of total haemoglobin and is the format used in the US, based on the DCCT clinical trial reference method. IFCC expresses HbA1c in millimoles per mole of total haemoglobin and is the standard in the UK, Europe, and Australia. The IFCC values are numerically lower. The conversion is: IFCC (mmol/mol) = (NGSP% − 2.15) × 10.929. So 7.0% NGSP = 53 mmol/mol IFCC. Both measure the same molecule with different reference systems.

What is eAG and how is it calculated?

eAG (estimated average glucose) translates your HbA1c into the familiar mg/dL or mmol/L units shown on a glucose meter. The formula comes from the ADAG study (Nathan et al., Diabetes Care, 2008), which used continuous glucose monitoring in 507 people across 10 sites. eAG (mg/dL) = 28.7 × HbA1c% − 46.7; eAG (mmol/L) = 1.59 × HbA1c% − 2.59. Because these are population-average equations, your personal value may differ by ±15–20 mg/dL due to individual variation in glycation rates and red cell lifespan.

What HbA1c should I aim for if I have diabetes?

For most non-pregnant adults with type 1 or type 2 diabetes, the ADA recommends an HbA1c target below 7.0% (53 mmol/mol). A target below 6.5% (48 mmol/mol) may be considered for younger people with a short disease duration. Targets above 8.0% (64 mmol/mol) may be appropriate for older adults, those with a history of severe hypoglycaemia, or significant comorbidities. For women with pre-existing diabetes during pregnancy, 6.0–6.5% (42–48 mmol/mol) is typically targeted. Always discuss personalised targets with your healthcare team.

Medical Disclaimer: This converter is provided for educational and informational purposes only. Conversion formulas follow the ADAG study (Nathan et al., Diabetes Care 2008) for eAG and the IFCC-NGSP consensus equation for unit conversion between % and mmol/mol. Individual HbA1c results may not accurately reflect true average glucose in people with haemoglobinopathies, certain types of anaemia, CKD, recent transfusion, or pregnancy. The eAG is a statistical estimate derived from a study population and may differ by ±15–20 mg/dL from your actual average glucose. Do not use this tool as a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider for interpretation of your laboratory results.

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