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What is A1C?
A1C (hemoglobin A1C, HbA1c, or glycated hemoglobin) is a blood test that provides a snapshot of your average blood sugar levels over the past 2 to 3 months. Unlike a fasting glucose test that captures a single moment, A1C reflects your overall blood sugar control over time.
The test measures the percentage of hemoglobin — the oxygen-carrying protein in red blood cells — that has glucose attached to it. Because red blood cells have a lifespan of approximately 120 days, the A1C test captures a weighted average of blood sugar levels during that period, with more recent weeks contributing more heavily.
The A1C test is the primary tool used by healthcare providers to diagnose prediabetes and diabetes, and to monitor how well diabetes treatment plans are working. The American Diabetes Association (ADA), the World Health Organization (WHO), and the International Diabetes Federation (IDF) all recommend A1C for diabetes diagnosis.
A1C Formula
This calculator uses the ADAG (A1C-Derived Average Glucose) formula developed by Nathan et al. and published in Diabetes Care in 2008. This is the formula recommended by the American Diabetes Association:
For mmol/L units:
Example 1: A1C of 5.7%
eAG = 28.7 × 5.7 − 46.7 = 163.59 − 46.7 = 116.9 mg/dL
This falls just below the prediabetes threshold (117 mg/dL), indicating a normal blood sugar level.
Example 2: A1C of 8.0%
eAG = 28.7 × 8.0 − 46.7 = 229.6 − 46.7 = 182.9 mg/dL
This is well above the diabetes threshold (140 mg/dL), indicating poorly controlled diabetes.
A1C Chart
The table below shows A1C values from 4% to 14% with their corresponding estimated average glucose in both mg/dL and mmol/L, IFCC values in mmol/mol, and diagnostic category.
| A1C (%) | eAG (mg/dL) | eAG (mmol/L) | IFCC (mmol/mol) | Category |
|---|---|---|---|---|
| 4.0% | 68.1 | 3.8 | 20.2 | Normal |
| 4.5% | 82.5 | 4.6 | 25.7 | Normal |
| 5.0% | 96.8 | 5.4 | 31.1 | Normal |
| 5.5% | 111.2 | 6.2 | 36.6 | Normal |
| 6.0% | 125.5 | 7.0 | 42.1 | Prediabetes |
| 6.5% | 139.8 | 7.8 | 47.5 | Diabetes |
| 7.0% | 154.2 | 8.6 | 53.0 | Diabetes |
| 7.5% | 168.6 | 9.4 | 58.5 | Diabetes |
| 8.0% | 182.9 | 10.2 | 63.9 | Diabetes |
| 8.5% | 197.3 | 11.0 | 69.4 | Diabetes |
| 9.0% | 211.6 | 11.8 | 74.9 | Diabetes |
| 9.5% | 226.0 | 12.6 | 80.3 | Diabetes |
| 10.0% | 240.3 | 13.3 | 85.8 | Diabetes |
| 10.5% | 254.7 | 14.1 | 91.3 | Diabetes |
| 11.0% | 269.0 | 14.9 | 96.7 | Diabetes |
| 11.5% | 283.4 | 15.7 | 102.2 | Diabetes |
| 12.0% | 297.7 | 16.5 | 107.7 | Diabetes |
| 12.5% | 312.1 | 17.3 | 113.1 | Diabetes |
| 13.0% | 326.4 | 18.1 | 118.6 | Diabetes |
| 13.5% | 340.8 | 18.9 | 124.0 | Diabetes |
| 14.0% | 355.1 | 19.7 | 129.5 | Diabetes |
Normal A1C Ranges
eAG below 117 mg/dL. Your blood sugar levels are in a healthy range. Maintain a balanced diet and regular physical activity.
eAG 117–137 mg/dL. You are at increased risk of developing type 2 diabetes. Lifestyle changes can help prevent progression.
eAG 140 mg/dL or higher. Consult your healthcare provider for diagnosis confirmation and treatment plan.
Frequently Asked Questions
What does A1C mean?
A1C (also called HbA1c or glycated hemoglobin) is a blood test that measures your average blood sugar level over the past 2 to 3 months. It reflects the percentage of hemoglobin proteins in your blood that are coated with sugar (glycated). The higher your blood sugar levels have been, the higher your A1C will be.
What is a normal A1C level?
A normal A1C level is below 5.7%. An A1C between 5.7% and 6.4% indicates prediabetes, meaning you are at increased risk of developing type 2 diabetes. An A1C of 6.5% or higher on two separate tests indicates diabetes. The American Diabetes Association (ADA) recommends a target A1C of less than 7% for most adults with diabetes.
How is A1C calculated?
The A1C test measures the percentage of hemoglobin in your blood that has glucose attached to it. To convert A1C to estimated average glucose (eAG), the ADAG formula is used: eAG (mg/dL) = 28.7 × A1C − 46.7. For example, an A1C of 7% corresponds to an eAG of approximately 154 mg/dL.
Is A1C the same as blood sugar?
No, A1C and blood sugar are related but different measurements. Blood sugar (glucose) tests measure your blood sugar at a single point in time. A1C reflects your average blood sugar over 2-3 months. Because A1C provides a longer-term picture, it is the preferred test for diagnosing and monitoring diabetes.
How often should I check A1C?
The ADA recommends A1C testing at least twice a year for people with diabetes who are meeting treatment goals, and quarterly (every 3 months) for people whose therapy has changed or who are not meeting blood sugar targets. For those without diabetes, testing may be done as part of routine health screenings.
What A1C level is dangerous?
An A1C above 9% is considered very high and significantly increases the risk of diabetes complications including nerve damage, kidney disease, eye problems, and cardiovascular disease. An A1C above 12% is extremely dangerous and requires immediate medical attention. Even A1C levels between 6.5% and 9% increase complication risks over time.
Can A1C be lowered?
Yes, A1C can be lowered through lifestyle changes and medical treatment. Key strategies include eating a balanced, low-glycemic diet, regular physical activity (at least 150 minutes per week), maintaining a healthy weight, managing stress, getting adequate sleep, and taking prescribed medications such as metformin or insulin as directed by your doctor.
How to Use This A1C Calculator
Getting your results with this A1C calculator is quick and straightforward. Start by entering your A1C percentage from your most recent lab results into the input field above. Your doctor or lab report will list this value as a percentage, typically between 4% and 14%.
Once you enter your value and click "Calculate," the tool instantly displays your estimated average glucose (eAG) in three formats: mg/dL (used primarily in the United States), mmol/L (used in most other countries), and IFCC mmol/mol (the international standard). This way, no matter which unit system your healthcare provider uses, you can understand your results.
The results are color-coded for easy interpretation. A green badge indicates a normal A1C level below 5.7%. A yellow badge signals prediabetes, meaning your A1C falls between 5.7% and 6.4%. A red badge indicates diabetes, with an A1C of 6.5% or higher. The visual gauge at the top of the results also shows where your A1C falls on the spectrum.
Your privacy is fully protected — all calculations happen directly in your browser and no data is ever sent to any server. Your health information remains completely private on your device.
For a complete reference of A1C values and their corresponding glucose levels, you can also use the A1C chart below to look up specific values and compare your results over time.
About This Calculator
Accurate Formula
Uses the clinically validated ADAG formula recommended by the American Diabetes Association (ADA).
Fast & Private
All calculations happen instantly in your browser. No data is sent to any server — your health information stays private.
Evidence-Based
Based on peer-reviewed research and ADA clinical guidelines. References linked in our footer.