A1C to eAG Calculator

What A1C and eAG Mean and Why Converting Helps

An A1C to eAG calculator is a translation tool. A1C (also called HbA1c) is a percentage that represents how much hemoglobin in your blood is glycated. Because red blood cells circulate for weeks, A1C reflects average glucose exposure over roughly the prior two to three months. That makes it extremely useful for monitoring long-term control and for seeing whether treatment changes are working over time.

The challenge is that A1C does not look like the numbers many people see every day. Glucose meters typically show results in mg/dL (common in the United States) or mmol/L (common in the UK and many other countries). Those daily readings are snapshots: a fasting value, a pre-meal value, a post-meal value, or a number taken during symptoms. A1C, in contrast, compresses many days of glucose exposure into one summary number.

Estimated average glucose (eAG) bridges that gap. It expresses an A1C result as an average glucose value in mg/dL (and often mmol/L), which can be easier to compare with what you see on a meter or continuous glucose monitor. This does not replace your day-to-day data, but it can reduce confusion, improve communication, and help you set realistic targets with your care team.

The ADAG Relationship Behind the A1C to eAG Formula

The most commonly cited conversion between A1C and eAG comes from the A1c-Derived Average Glucose (ADAG) study relationship, which established a strong linear link between measured average glucose and A1C across a large dataset. That relationship is usually written as: eAG (mg/dL) = 28.7 × A1C − 46.7.

This is the equation used in many clinical references and calculators. It produces an estimated average glucose in mg/dL. To express the result in mmol/L, the tool converts mg/dL to mmol/L using the standard glucose conversion factor, then rounds the output to match typical reporting style (whole numbers in mg/dL and one decimal in mmol/L).

It’s important to understand what the equation is and what it is not. It is a statistical translation based on population data. It does not “read” your meter or your CGM, and it does not know whether your average came from stable numbers or big swings between highs and lows. Two people can share the same A1C and have very different daily patterns. That is why the conversion is best used for communication and planning, not as a complete picture of glucose management.

Why Your eAG and Your Meter Average May Not Match

If you compare eAG with an app “average glucose” from fingersticks or CGM, it is common to notice differences. Several factors explain why:

• Time window mismatch: A1C reflects weeks to months, while your meter average may reflect days or the period you chose.
• Sampling bias: fingerstick readings often miss overnight data or post-meal peaks unless you test at those times.
• Variability: frequent swings can “average out” into a similar A1C while still creating high-risk patterns.
• Physiology and lab differences: A1C is influenced by red blood cell lifespan and certain medical conditions.

When eAG and observed averages differ, the next step is usually context, not panic. Confirm unit settings, check that your average window is comparable, and talk with a clinician if the mismatch persists, especially if there are conditions that can distort A1C.

NGSP (%) vs IFCC (mmol/mol) and Why Both Units Exist

A1C is reported in two common unit systems. NGSP (sometimes called DCCT-aligned) reports A1C as a percentage. IFCC reports HbA1c as mmol/mol. Many labs outside the U.S. primarily use IFCC units, while many U.S. reports use NGSP units. If you move between countries or compare older and newer reports, you may see both.

This calculator converts between the two using a standard linear relationship (often called the master equation). The tool always shows both values in results so you can match your lab report format and communicate clearly.

How to Use This Calculator for Targets and Goal Planning

Conversions are most useful when they help you take action. Here are practical ways to use each tab:

• A1C → eAG: translate a lab result into mg/dL and mmol/L so it makes sense alongside daily readings.
• eAG → A1C: estimate what an average glucose value implies in A1C terms (useful for goal discussions).
• Conversion Table: build a quick reference chart (for travel, education, or explaining results).
• Ranges & Goals: compare an A1C to common ADA-style categories and translate a target A1C into a target eAG number.

Many people find goal translation particularly helpful: if a clinician recommends a target A1C, translating it to eAG can make the goal feel concrete. For example, an A1C of 7% corresponds to an eAG near 154 mg/dL, which can be easier to relate to pre-meal and post-meal numbers.

Interpreting Categories Carefully and Keeping Context

A1C categories (normal, prediabetes, diabetes) are widely used, but interpretation still requires context. Diagnosis is typically confirmed by repeat testing or by using multiple measures depending on symptoms and clinical scenario. Also, targets vary by individual: some people aim for tighter control if it can be achieved safely, while others need a higher target because avoiding hypoglycemia, simplifying therapy, or managing multiple conditions is the priority.

A good mental model is: A1C is a trend indicator, eAG is a translation, and daily glucose data shows the pattern. Together they give a clearer picture than any single number.

When A1C May Be Less Reliable

A1C assumes a typical red blood cell lifespan and typical hemoglobin behavior. If those assumptions are broken, A1C can read higher or lower than true glucose exposure. Examples include some hemoglobin variants, anemia or recent blood loss, pregnancy, kidney disease, and recent transfusion. If your A1C does not “fit” your meter/CGM data, ask about alternate assessments such as fructosamine, CGM metrics, or lab review of hemoglobin variants.

How to Use the Conversion Table for Fast Communication

The conversion table is designed for real-world convenience. If you are teaching someone, discussing targets at a visit, or comparing documents that use different unit systems, having a table can reduce errors. Keep the table’s range realistic (for example, 5% to 12% A1C) and choose a step (0.5% is common) so it stays readable.

If you prefer IFCC units, you can build the table by mmol/mol instead. The calculator will generate the matching NGSP percentage and both eAG unit outputs.