A1C Calculator

Q: How accurate is the A1C to eAG conversion?

The ADAG formula fits 507 individuals with a 95% CI of ±15 mg/dL. Individual glycation rates vary, so the number is a good average but any single reading has natural spread. CGM data over 14 days is the more precise picture of glucose exposure.

Q: Why does A1C not reflect my recent glucose?

Red blood cells live ~120 days and A1C is their average glycation. About 50% of the A1C signal comes from the last 30 days, 25% from days 30–60, and 25% from days 60–120. A one-week binge or a one-week fast will not move A1C much; sustained changes over 6–8 weeks will.

Q: What A1C target should I aim for?

General ADA target for adults with diabetes is <7%. Older adults, frail patients, or those with severe hypoglycemia history often target 7.5–8%. Younger, otherwise healthy patients may target <6.5%. Individualize with the care team; overly-tight targets increase hypoglycemia risk.

Q: Can non-diabetes conditions affect A1C?

Yes. Hemoglobin variants (SS, SC, thalassemia), iron deficiency, kidney failure, recent transfusion, and pregnancy can all skew A1C. When suspected, fructosamine (2–3 week glucose average) or 14-day CGM is used instead.

Convert HbA1c to estimated average blood glucose (eAG) or the other way, using the ADAG standard formula. Interpretation bands cover normal, prediabetes, and diabetes thresholds.

Last updated: October 2026

Direction

HbA1c (%) (optional)

Average glucose (eAG) (mg/dL) (optional)

Estimated result

116.89 mg/dL

This calculator gives an estimate for general information only. It is not medical advice and does not replace a doctor, pharmacist or other qualified health professional. Always check with them before acting on the result, especially for medication doses, children, pregnancy or a medical condition, and follow the guidelines of your local health authority.

Formula below · 3 sources (niddk.nih.gov, diabetesjournals.org, care.diabetesjournals.org) · Updated Oct 2026

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About this calculator

HbA1c (glycated hemoglobin) measures the average blood glucose exposure of hemoglobin over the red blood cell lifespan (~120 days). The ADAG (A1C-Derived Average Glucose) study (Nathan et al., 2008) established the near-linear conversion: eAG (mg/dL) = 28.7 × A1C(%) − 46.7. This calculator uses that exact formula in both directions. Pick the direction, then fill in only the box for the value you have (HbA1c for A1C → eAG, average glucose for eAG → A1C); the other box can stay empty.

The ADA diagnostic thresholds are: <5.7% normal, 5.7–6.4% prediabetes, ≥6.5% diabetes on two confirming tests. HbA1c is not a real-time glucose reading — it is a rolling ~3-month average, weighted more toward the most recent month. Conditions that shorten red-cell lifespan (hemolytic anemia, recent transfusion, hemoglobin variants like SS, SC, or thalassemia) can produce falsely low A1C for the actual glucose average, and iron-deficiency anemia can raise it. In those cases, fructosamine or continuous glucose monitoring (CGM) is used instead.

A useful anchor point: A1C 6% ≈ 126 mg/dL average, A1C 7% ≈ 154, A1C 8% ≈ 183 mg/dL. Each 1% rise in A1C corresponds to about 29 mg/dL higher average glucose.

Other units. Laboratories outside the US report HbA1c in IFCC mmol/mol, linked to the percent scale by the NGSP–IFCC master equation, IFCC = (A1C % − 2.15) × 10.929, so 7% is 53 mmol/mol; and the ADAG study also gives the average glucose in mmol/L as 1.59 × A1C − 2.59. Both appear as tiles under the result, and the A1C to mmol/mol converter and the GMI calculator (A1C-equivalent from a CGM average) cover those conversions in full.

How to use

Example — A1C 5.7% to eAG. eAG = 28.7 × 5.7 − 46.7 = 163.6 − 46.7 = 116.9 mg/dL. This is the borderline normal-to-prediabetes reading; consider lifestyle intervention. Example — average glucose 154 mg/dL to A1C. A1C = (154 + 46.7) / 28.7 = 200.7 / 28.7 = 6.99%, essentially 7.0%. That is a common target for adults with type 2 diabetes on treatment per ADA Standards of Care.

Frequently asked questions

How accurate is the A1C to eAG conversion?

The ADAG formula fits 507 individuals with a 95% CI of ±15 mg/dL. Individual glycation rates vary, so the number is a good average but any single reading has natural spread. CGM data over 14 days is the more precise picture of glucose exposure.

Why does A1C not reflect my recent glucose?

Red blood cells live ~120 days and A1C is their average glycation. About 50% of the A1C signal comes from the last 30 days, 25% from days 30–60, and 25% from days 60–120. A one-week binge or a one-week fast will not move A1C much; sustained changes over 6–8 weeks will.

What A1C target should I aim for?

General ADA target for adults with diabetes is <7%. Older adults, frail patients, or those with severe hypoglycemia history often target 7.5–8%. Younger, otherwise healthy patients may target <6.5%. Individualize with the care team; overly-tight targets increase hypoglycemia risk.

Can non-diabetes conditions affect A1C?

Yes. Hemoglobin variants (SS, SC, thalassemia), iron deficiency, kidney failure, recent transfusion, and pregnancy can all skew A1C. When suspected, fructosamine (2–3 week glucose average) or 14-day CGM is used instead.

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