Estimate your A1C from average blood glucose, or convert an A1C result to estimated average blood sugar. A1C reflects your average blood sugar over the past 2-3 months.
A1C (also called HbA1c or glycated hemoglobin) measures the percentage of your red blood cells that have glucose attached. Since red blood cells live about 120 days, A1C reflects your average blood sugar over the past 2-3 months — it is far more useful than a single fasting glucose reading, which only captures one moment in time.
Why it matters: A1C is the primary marker used to diagnose and monitor prediabetes and type 2 diabetes. An A1C of 5.7% or higher signals that your blood sugar has been elevated on average. Every 1% drop in A1C is associated with significant reduction in microvascular complications.
If your A1C is normal (<5.7%), testing every 1-2 years is sufficient. If you are in the prediabetic range (5.7-6.4%), test every 3-6 months to track if lifestyle changes are working. For diagnosed diabetes, the ADA recommends testing A1C every 3 months until stable, then at least twice a year.
Limitations: A1C can be inaccurate in conditions that affect red blood cell turnover (e.g., iron deficiency anemia, sickle cell trait, recent blood loss). In these cases, fructosamine or continuous glucose monitoring (CGM) may provide better data.
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Start Tracking FreeThis calculator is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider for interpretation of lab results and treatment decisions.