A1C Calculator
Convert between HbA1c percentage and estimated average glucose using the ADA-recommended ADAG formula
Enter your HbA1c percentage as reported on a US lab report (DCCT/NGSP standard). Range: 4.0 to 14.0%
Optional: Enter A1C in the international IFCC standard (European labs). Range: 20 to 130 mmol/mol
Calculate Your A1C
Enter your A1C percentage or average glucose reading above to see the conversion, risk classification, and personalized health context.
How to Use the A1C Calculator
Choose Your Calculation Direction
Select 'A1C to Glucose' if you have your HbA1c lab result and want to see the equivalent average blood sugar in mg/dL or mmol/L. Select 'Glucose to A1C' if you have been tracking your average blood glucose readings (from a home glucometer or CGM) and want to estimate what your A1C might be.
Enter Your Value
In A1C to Glucose mode, enter your HbA1c percentage as shown on your lab report — for example, 7.0. US lab reports use the NGSP percentage scale. If you have a European lab report showing mmol/mol, enter that value in the IFCC field instead. In Glucose to A1C mode, enter your average blood glucose and select whether it is in mg/dL or mmol/L.
Review All Four Outputs
After calculating, you will see four values simultaneously: your A1C in NGSP percent, your A1C in IFCC mmol/mol, your estimated average glucose in mg/dL, and your estimated average glucose in mmol/L. This lets you compare values across different measurement standards used by different countries and laboratories.
Understand Your Risk Classification and Reference Table
Read your ADA risk classification (Normal, Prediabetes, Diabetes, or higher), the contextual explanation of what it means, and the comparison to the ADA target of 7.0% for most adults. Check the A1C spectrum bar to see visually where your value sits. Scroll down to the reference table to see how your value compares to the full A1C scale from 4% to 13%, with your current row highlighted.
Frequently Asked Questions
What is a normal A1C level, and what do the different ranges mean?
A normal A1C is below 5.7%, which corresponds to an average blood sugar of about 117 mg/dL or less. This range indicates healthy glucose metabolism with no signs of prediabetes or diabetes. Prediabetes is defined as an A1C between 5.7% and 6.4%, corresponding to average glucose of approximately 117 to 137 mg/dL. This is a warning zone where blood sugar regulation is impaired but has not yet crossed the diabetes threshold. Diabetes is diagnosed at 6.5% or higher on two separate tests, equivalent to an average glucose of about 140 mg/dL or above. For people already diagnosed with diabetes, the ADA recommends keeping A1C below 7.0% (eAG under 154 mg/dL) to minimize the risk of complications. More relaxed targets of below 8.0% may be set for older adults or those with complex health situations.
How often should I get my A1C tested?
The testing frequency depends on your situation. For people with well-controlled diabetes who are meeting their A1C targets, the ADA recommends testing every six months. For people whose treatment has recently changed or who are not meeting glycemic goals, testing every three months is appropriate so that adjustments can be made more quickly. For people who have prediabetes, annual A1C testing is generally recommended to monitor whether blood sugar is improving or worsening. For people without diabetes and with no known risk factors, testing every three years is sufficient once an initial baseline has been established. Your healthcare provider will determine the right schedule based on your specific circumstances, medications, and glycemic control history.
Can I lower my A1C, and how long does it take to see results?
Yes, A1C can be meaningfully reduced through lifestyle changes and, when appropriate, medication. The most effective lifestyle interventions are consistent aerobic exercise (at least 150 minutes per week of moderate-intensity activity), a diet low in refined carbohydrates and added sugars, weight loss (even 5 to 10% of body weight significantly improves insulin sensitivity), and reducing portion sizes of high-glycemic foods. Because A1C reflects a 90-day average, it takes at least two to three months to see measurable changes after making improvements. However, blood glucose levels themselves begin improving within days of starting lifestyle changes. Some people with prediabetes can return to normal A1C through diet and exercise alone. Medication including metformin, GLP-1 agonists, SGLT-2 inhibitors, and insulin can also substantially reduce A1C when prescribed by a physician.
Why is my A1C different from what I would expect based on my blood sugar readings?
Several factors can cause a disconnect between your home glucose readings and your A1C result. First, A1C reflects all hours of the day and night, including post-meal peaks and overnight values that home monitors may miss if you only check at certain times. A continuous glucose monitor (CGM) provides a more complete picture of total glucose exposure. Second, certain medical conditions can artificially alter A1C: hemolytic anemia, sickle cell trait, and iron or B12 deficiency can cause A1C to read falsely lower or higher than your actual average glucose warrants. Third, research has shown that some ethnic groups, particularly African American individuals, may have naturally higher A1C at the same average glucose level. If your A1C seems inconsistent with your daily glucose logs, discuss this with your provider. They may consider alternative measures such as fructosamine or a glucose management indicator (GMI) from a CGM.
What is the difference between NGSP percent and IFCC mmol/mol?
NGSP (National Glycohemoglobin Standardization Program) percentage and IFCC (International Federation of Clinical Chemistry) mmol/mol are two different measurement standards for the same test, similar to how Celsius and Fahrenheit both measure temperature. The NGSP percentage scale, also called the DCCT scale, is used primarily in the United States, Canada, and Japan. The IFCC mmol/mol scale is used in most European countries, Australia, and many other international settings. They report the same underlying measurement, but in different units. The conversion is: IFCC (mmol/mol) = 10.929 × (NGSP% − 2.15). For example, an A1C of 7.0% NGSP equals approximately 53 mmol/mol IFCC. This calculator shows both values simultaneously so you can interpret results regardless of which standard your laboratory uses.
Is the A1C test the same as a fasting blood glucose test?
No, they measure different things. A fasting blood glucose test captures your blood sugar at a single moment after at least eight hours without food. It shows what your baseline glucose is when you have not eaten, and it can vary significantly from day to day based on stress, sleep, illness, and other factors. The A1C test, by contrast, reflects the cumulative effect of your blood sugar over the past two to three months and is not affected by what you ate the day before or whether you fasted. Both tests are valuable for different reasons. Fasting glucose is useful for day-to-day management decisions, while A1C provides the long-term view that predicts complication risk. The ADA recommends using A1C as the primary diagnostic and monitoring tool because it is more stable and does not require fasting, though both fasting glucose and A1C can be used for diabetes diagnosis.