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A1c Calculator

Health

Estimate your hemoglobin A1c percentage from average blood glucose using the inverse ADAG formula, with ADA diagnostic category context included instantly.

Average Blood Glucose
mg/dL
50 mg/dL400 mg/dL

Use your average glucose meter or continuous glucose monitor (CGM) reading over several weeks for the most representative estimate.

Estimated A1c

0%

ADA Category

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For informational purposes only. A lab-drawn A1c test is required for an official diagnosis — consult a healthcare provider.

What is a A1c Calculator?

An A1c Calculator estimates your hemoglobin A1c percentage from an average blood glucose reading, using the inverse of the ADAG (A1c-Derived Average Glucose) study formula. A1c reflects the percentage of hemoglobin in red blood cells that has glucose attached, and because red blood cells circulate for roughly three months, it captures average glucose exposure over that period rather than any single reading.

This calculator runs the ADAG relationship in reverse from the Estimated Average Glucose Calculator, which converts A1c into an average glucose figure — together the two tools let you move between average glucose and A1c in either direction. It also applies American Diabetes Association diagnostic thresholds to give immediate category context.

How to use this A1c Calculator calculator

  1. Gather your Average Blood Glucose reading — ideally averaged over several weeks of consistent glucose meter or CGM data.
  2. Enter that value into the Average Blood Glucose field.
  3. Review the Estimated A1c result, shown as the primary output in percentage form.
  4. Check the A1c Category to see whether the estimate falls in the normal, prediabetes, or diabetes range.
  5. Compare the result to your most recent lab-drawn A1c if available, and discuss any notable differences with your healthcare provider.

Formula & Methodology

Estimated A1c (%) = (Average Glucose in mg/dL + 46.7) ÷ 28.7

This is the inverse of the ADAG study formula (Nathan et al., Diabetes Care, 2008): eAG(mg/dL) = 28.7 × A1c − 46.7, rearranged to solve for A1c given an average glucose value.

Diagnostic categories follow ADA criteria: Normal is below 5.7%, Prediabetes is 5.7%-6.4%, and Diabetes range is 6.5% or above.

Worked example: for an average blood glucose of 150 mg/dL:
- Estimated A1c = (150 + 46.7) ÷ 28.7 = 6.85%
- Since 6.85% is at or above 6.5%, the category shown is Diabetes range.

For a fuller definition, see our glossary entry on A1C.

Frequently Asked Questions

The A1c test (also called hemoglobin A1c or HbA1c) measures the percentage of hemoglobin proteins in red blood cells that have glucose attached to them. Because red blood cells live for about three months, A1c reflects average blood glucose exposure over that period rather than a single point-in-time reading.
This calculator uses the inverse of the ADAG (A1c-Derived Average Glucose) study formula: A1c equals your average glucose in mg/dL plus 46.7, divided by 28.7. This is the same relationship labs use in reverse when reporting estimated average glucose (eAG) alongside an A1c result.
According to the American Diabetes Association, an A1c below 5.7% is considered normal, 5.7% to 6.4% falls in the prediabetes range, and 6.5% or higher meets the diagnostic threshold for diabetes. This calculator applies those same category thresholds to the estimated A1c result.
Yes, entering your average blood glucose reading — ideally averaged over several weeks of consistent testing — gives a reasonable estimate of what your A1c might show. However, an actual A1c blood test remains the definitive measure, since meter averages depend heavily on testing frequency and timing.
Differences can arise because meter or CGM averages only capture the periods you actually tested, while a lab A1c reflects a true three-month average across all hours of the day. Conditions affecting red blood cell lifespan, such as anemia or certain blood disorders, can also cause lab A1c to diverge from the ADAG-predicted value.
This calculator converts average glucose into an estimated A1c, while the [Estimated Average Glucose Calculator](/estimated-average-glucose-calculator/) does the reverse, converting A1c into an average glucose figure. Both use the same underlying ADAG formula, just applied in opposite directions depending on which value you already have.
The American Diabetes Association generally recommends A1c testing at least twice a year for people with stable, well-controlled diabetes, and quarterly for those adjusting treatment or not meeting glucose targets. Your healthcare provider can recommend the right testing schedule for your situation.
A1c reflects an overall average and does not distinguish between stable glucose levels and levels that swing widely between highs and lows. Two people can have the same A1c with very different day-to-day glucose patterns, which is why continuous glucose monitoring is sometimes used alongside A1c for a fuller picture.
A1c reflects glucose control over time, while measures like the [HOMA-IR Calculator](/homa-ir-calculator/) estimate insulin resistance from a single fasting glucose and insulin measurement. Elevated A1c and insulin resistance often occur together but measure different aspects of metabolic health.
No — this calculator provides an educational estimate only and cannot diagnose diabetes or prediabetes. An official diagnosis requires laboratory-confirmed A1c, fasting glucose, or oral glucose tolerance testing interpreted by a qualified healthcare provider.
Also known as
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