Estimated Average Glucose Calculator

How it is calculated

The tool applies the linear equation from the ADAG study: eAG (mg/dL) = 28.7 × A1c − 46.7, where A1c is the HbA1c result in percent. The value in mmol/L is then eAG (mg/dL) ÷ 18. The mg/dL figure is rounded to a whole number and the mmol/L figure to one decimal, and the mmol/L value is calculated from the unrounded mg/dL value, so converting the rounded number by hand can differ by 0.1. The result is only an average estimated from a lab percentage, not a measured meter reading. Any number above zero is accepted without a plausibility check: very low values give a negative eAG (an A1c of 1 gives −18 mg/dL), which has no real meaning, so enter only a genuine HbA1c percentage. The tool does not take HbA1c in mmol/mol.

Common mistakes

• Entering the HbA1c in mmol/mol (for example 53) instead of percent (7). The tool expects percent and would return 1,474 mg/dL for 53, which is clearly wrong.
• Treating the eAG as the glucose reading on a given day. It is an average over the weeks behind the HbA1c, and a meter can read much higher or lower at any one moment.
• Typing the percent as a fraction, such as 0.07. The field takes the number as printed on the lab report, so 7 for 7%.
• Expecting meter averages to match eAG exactly. The formula is a statistical relationship, so an individual's real average can differ from the estimate.
• Mixing up the two result units. Dividing mg/dL by 18 gives mmol/L; a result of 8.6 mmol/L and 154 mg/dL are the same glucose level, not two different readings.