HbA1c (%)

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eAG trend across A1c checkpoints 4.0, 5.6, 6.0 and 6.5 percent — Every 0.1% A1c change moves eAG by 2.87 mg/dL.

Method & verification

How This Tool Works

fact-checked against our calculation methodology

Calculation Method

Computes eAG from HbA1c.

Site methodology

BoringToolsKit methodology and verification standard

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Assumptions to Verify

These tools provide general estimates for planning and education only.
They are not medical advice and not a substitute for a qualified healthcare professional.
Always consult your doctor or another healthcare provider about your specific situation.

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Worked examples at three checkpoints

The formula is linear, so every 0.1% change in A1c moves eAG by exactly 2.87 mg/dL. Take A1c 5.6%, the top of the normal band: 28.7 x 5.6 = 160.72, then 160.72 - 46.7 = 114.02, which rounds to 114 mg/dL. At A1c 6.0% (prediabetes range): 28.7 x 6.0 = 172.2, minus 46.7 gives 125.5, rounding to 126 mg/dL.

Now the diabetes threshold at 6.5%: 28.7 x 6.5 = 186.55, then 186.55 - 46.7 = 139.85, or 140 mg/dL. That 14 mg/dL jump between the 6.0 and 6.5 results is what a single half-point A1c rise costs. A practical checkpoint: if your lab report shows A1c 6.4%, the calculator gives 28.7 x 6.4 = 183.68 - 46.7 = 136.98, about 137 mg/dL, one step below the 6.5% cutoff. If your meter's 14-day or 30-day average reads wildly different from that eAG, the mismatch itself is data, and it usually means glucose is swinging rather than sitting flat.

Where the estimate breaks down

The 28.7/-46.7 line is a population regression from the ADAG study (about 1,400 participants), so it is a fitted average, not a per-person law. The study's own scatter shows individuals at the same A1c landing roughly 30 to 40 mg/dL apart in true average glucose. Red blood cell lifespan is the main culprit: hemolytic anemia shortens cell life and makes A1c read falsely low, while iron deficiency anemia can push it falsely high. Pregnancy, recent blood loss, and kidney dialysis shift it too.

Edge cases in the calculator itself: it accepts 3.0% to 15.0% and rejects anything outside. Below 3% is not a plausible lab value and above 15% (eAG about 384 mg/dL) the linear fit loses accuracy, since the ADAG cohort rarely included extremes. Note the asymmetry of the formula: at A1c 4.0% it computes an eAG of 68 mg/dL, which is below most meters' usable floor of 40 mg/dL, so treat low-range outputs as directional only. The output is an estimate of average glucose over the prior 2 to 3 months, not a diagnosis, and CGM users should compare it against their own 90-day GMI rather than trusting the population curve.