Hemoglobin A1C measures the percentage of hemoglobin molecules in red blood cells that have glucose attached, reflecting average blood glucose over the preceding 2-3 months (red blood cell lifespan). Estimated Average Glucose (eAG) converts that percentage into the same units (mg/dL or mmol/L) used in daily glucose monitoring. The conversion uses the ADAG formula: eAG (mg/dL) = 28.7 × A1C - 46.7. For example, an A1C of 7.0% converts to eAG of 154 mg/dL (8.6 mmol/L). While A1C provides a long-term average, eAG translates it into actionable daily glucose numbers that align with meter readings and help patients understand what their A1C means in practical terms.

The ADAG formula has excellent accuracy for most individuals with diabetes: within ±15% of actual mean glucose 95% of the time. The formula was derived from continuous glucose monitoring (CGM) data correlating with A1C measurements in 507 individuals across diverse populations. However, accuracy can be affected by several factors: Hemoglobin variants (sickle cell, thalassemia) that affect A1C measurement; Conditions affecting red blood cell turnover (anemia, kidney disease, pregnancy); Recent blood transfusions; and Extreme glucose variability (labile diabetes). Therefore, our calculator flags these conditions and suggests when A1C may not accurately reflect average glucose. For most individuals without these conditions, the conversion provides reliable glucose estimation.

Several factors can create discrepancies between calculated eAG and daily glucose averages. First, timing of readings - if you test mainly fasting or pre-meal, you'll miss postprandial spikes. Second, glucose variability - high variability (rollercoaster patterns) can yield same A1C as stable pattern but different symptom experience. Additionally, meter accuracy - home glucose meters have ±15% accuracy limits; Testing frequency - infrequent testing misses highs/lows; Hemoglobin factors - conditions affecting A1C accuracy. Consequently, our calculator helps identify these discrepancies by comparing your meter average to calculated eAG and suggesting optimal testing patterns. Continuous glucose monitoring (CGM) provides the most accurate comparison, capturing 96% of glucose variability.

eAG provides actionable targets for daily management in several ways. For instance, you can set realistic goals - if A1C target is 7.0%, aim for average glucose ~154 mg/dL. Moreover, it helps identify patterns - compare time-of-day readings to eAG to spot problem periods. Additionally, you can adjust medications - use eAG to guide insulin or medication titration; Educate about targets - understand what glucose ranges correspond to A1C goals; Motivate behavior change - seeing glucose equivalents makes abstract percentages tangible. Accordingly, our calculator provides personalized recommendations based on your conversion results, including suggested glucose ranges, time-in-range targets, and medication adjustment considerations. Regular conversion (every 3 months with A1C testing) helps track progress toward goals.

While the ADAG formula is standard, alternative equations exist for specific situations. For example, older formulas like DCCT-derived (eAG = (A1C × 35.6) - 77.3) yield slightly different results. Similarly, pediatric adjustments may be needed as red blood cell lifespan differs in children. Additionally, population-specific formulas have been proposed for certain ethnic groups; Linear vs. non-linear relationships at A1C extremes (<6% or >10%). Therefore, our calculator provides multiple conversions for comparison and identifies when alternative formulas might be more appropriate. The ADAG formula remains the internationally recognized standard endorsed by ADA, EASD, and IDF for clinical use. We also provide the newer "glucose management indicator" (GMI) from CGM data for comparison when available.