What Is A1C and eAG? Understanding Your 3‑Month Blood Sugar

Guides · Health · Updated 2026

If you've ever had a diabetes screening or manage blood sugar, you've likely heard of the A1C test. Unlike a finger‑stick that gives a single moment's reading, the hemoglobin A1C test reflects your average blood glucose over the past 2–3 months. Because percentages like "7%" are less intuitive, doctors often translate A1C into an estimated average glucose (eAG) in familiar mg/dL or mmol/L. This guide explains how the test works, the A1C‑to‑eAG formula, and what the numbers mean at every level from 5 to 12%.

Why A1C Is a 3‑Month Average

Glucose in your bloodstream attaches to hemoglobin, the oxygen‑carrying protein inside red blood cells. The more glucose present, the higher the percentage of "glycated" hemoglobin. Since red blood cells live about 120 days, the A1C captures a weighted average of glucose levels — more recent weeks influence it slightly more. That's why the test is done quarterly for people with diabetes: it shows long‑term trends, not just the fasting number you had this morning.

• A1C below 5.7% is considered normal.
• 5.7%–6.4% indicates pre‑diabetes.
• 6.5% or above on two separate tests confirms diabetes.

Step-by-step: Convert A1C to eAG

1. Open the A1C Calculator tool.
2. Enter your A1C percentage (e.g., 6.2%). You can also enter an eAG value to reverse‑calculate the A1C.
3. The tool applies the ADAG formula (eAG = 28.7 × A1C - 46.7) and shows your estimated average glucose in both mg/dL and mmol/L.
4. It also labels the result as normal, pre‑diabetic, or diabetic, providing a clear interpretation without medical jargon.

The eAG Formula & A1C 5–12 Table

For converting individual finger‑stick readings between units, use the Blood Sugar Converter. Together, these tools give you both the moment‑in‑time and the long‑term view.

Frequently Asked Questions

How often should I check my A1C?

If you have diabetes, every 3 months is standard. For pre‑diabetes or low risk, once a year may be enough. Follow your doctor's recommended frequency.

Can A1C be high without diabetes?

Yes. Conditions like iron‑deficiency anemia or certain hemoglobinopathies can falsely elevate A1C. If results don't match your glucose logs, discuss with your doctor.

Is eAG the same as average glucose on my meter?

eAG is derived from A1C and represents a calculated 24‑hour average, including post‑meal peaks. Your meter average may differ because you check at specific times.

What A1C should I target if I have diabetes?

Most guidelines recommend below 7%, but elderly or frail patients may have less strict targets. Personalisation is key — set the goal with your healthcare team.

Is it free and private?

Yes — the tool runs entirely in your browser, free, with no sign‑up and nothing uploaded to a server.

This article is educational. A1C testing and diabetes management should be supervised by a qualified physician. Do not change medications based on tool outputs alone.