How to Calculate Your A1C Levels [+Try our A1C Calculator]

If you’ve recently taken a blood test or you’ve been discussing glucose levels with your doctor, you may be familiar with the A1C test. The results of an A1C test may help provide an approximation of how much glucose has been in your bloodstream on average for the past two to three months. 

Why is it important to be aware of your A1C level? For one, the A1C test is one of the most common ways that healthcare professionals diagnose conditions such as prediabetes and type 2 diabetes. If you’re at risk of developing type 2 diabetes, this test may be something your healthcare provider recommends paying more attention to.

While only a lab test can accurately measure your A1C value (otherwise known as HbA1C), it’s also possible to calculate a general estimate of your A1C at home. In this article, we’ll dive deeper into exactly what A1C is, why it’s important, and how you can estimate your A1C level with our handy A1C calculator.

What Does A1C Actually Measure?

The A1C test measures the amount of glucose bound to hemoglobin in the blood (or glycated hemoglobin) over the three month lifetime of your blood cells. This blood test allows you to determine  what your average blood glucose levels are over time and can be measured through routine lab work. 

An A1C test result will appear as a percentage, with normal levels considered to be below 5.7 percent. According to the CDC, having A1C values within this normal range may be able to help reduce your risk of diabetes.

An A1C value differs from the glucose insights you would get from a glucometer or continuous glucose monitor (CGM). Measurements from these tools are reported in mg/dL or mmol/L, and measure the concentration of blood sugar in your bloodstream at a given moment.

These tools can be helpful for recognizing instances of hypoglycemia (low blood sugar) as they occur, or hyperglycemia (high blood sugar) after eating a meal. CGMs can also be particularly helpful in tracking glycemic variability, or how your glucose fluctuates in real time. A1C does not measure glycemic variability. 

How to Find Your A1C on Lab Results

While many routine blood tests measure things like your lipid levels or red and white blood cell count, an A1C test will usually need to be specifically requested by you and your doctor. This test is known as an HbA1C test, and unlike other types of blood tests, fasting is not required beforehand.

The A1C test is primarily used as a way to diagnose prediabetes or type 2 diabetes, and can also be helpful to track your progress if your goal is to lower your elevated A1C levels to a more “ideal” range.

The Difference Between Estimated Average Glucose and A1C

A1C is a measurement of glycated hemoglobin, and is reported as a percentage of your average blood sugar level. Estimated average glucose (or eAG), on the other hand, is a value calculated from your A1C value and is measured in mg/dL or mmol/L.

For more information on what these values signify, read our article on normal blood sugar levels.

As we mentioned, your A1C value is an average of the glucose in your blood during a two or three month period in which your red blood cells are alive. Because A1C represents sugar levels over an extended amount of time, your doctor can use this to get a general idea of your blood sugar control over time. 

However, it’s important to note that hemoglobin A1C is not a measure of the exact concentration of glucose in your blood. It is instead a measure of the percent of hemoglobin that has glucose bound to it. 

While A1C can be a helpful tool to estimate how your blood sugar has been on average, there are some outside factors that may skew the accuracy of your A1C reading, such as certain medications or health conditions.

What is Estimated Average Glucose?

Like A1C, your estimated average glucose (or eAG) measures the average levels of your blood sugar over a few months. This measurement is helpful for anyone interested in learning about their blood sugar levels, since eAG is a measurement of mg/dL or mmol/L, the same units used on any glucometer or CGM. However, this is just an estimate derived from A1C, and not a precise measurement.

You may have had your doctor explain your A1C levels in terms of estimated average glucose, or eAG. Estimated average glucose that falls below 126 mg/dL is considered normal by researchers and medical professionals. Just like with A1C, regularly checking your eAG may give you a more accurate representation of your blood sugar response over time. 

However, eAG may not always correspond accurately to fasting glucose (FPG) levels. In a 2022 study published in the journal Healthcare, researchers found that the proportion of subjects with a higher value of FPG than eAG was 46.3 percent in poorly controlled diabetic patients, compared with only 1.5 percent in normoglycemic subjects.

If your A1C or eAG is out of the normal range, you may want to speak with a doctor about what factors may be causing your elevated levels and how they may affect your well-being. You may also want to ask your doctor about the need for testing your fasting glucose (FPG) levels. 

Simple Conversion Formula for A1C From Average Blood Glucose

Now that you know what A1C is and what it measures, here’s how you can calculate it using your average glucose level. Luckily, it’s fairly simple to estimate your A1C percentage using a formula no more complicated than converting Celsius to Fahrenheit.

Keep in mind that blood glucose is measured in different ways depending on where you live. In the United States, you’ll find levels measured in mg/dL, while other countries generally use mmol/L. To calculate your A1C value, all you need to do is apply your average blood glucose measurement to one of the following formulas:

Try Our A1C Calculator

Not everyone loves crunching numbers. Instead, try calculating an estimation of your A1C value using our handy A1C calculator. 

Now that you have your A1C value, let’s take a closer look at how you can understand your A1C calculation. Later on, we’ll explain a few other ways you can test your A1C, either in a lab or at home.

Understanding Your A1C Level

Once you have an estimate of your A1C, check whether your levels are outside of the normal range by comparing your result to the ranges used by both the American Diabetes Association (ADA) and the CDC as shown below. Remember, it’s only possible to see a rough estimate when calculating your A1C, as any calculator will use your eAG value to determine your A1C.

If your estimated range falls anywhere above 5.7 percent, you may want to visit your doctor to learn more about the factors that can affect your blood sugar response. There are a number of lifestyle changes that may be beneficial as you work to lower your levels over time. 

One way to detect imbalances and fluctuations in glucose to see its impact on your overall health is by using a tool such as a continuous glucose monitor. If your A1C is out of the ideal range, your doctor may also help you set an A1C goal to aim for.

Now let’s take a closer look at how you can understand your A1C calculation, and a few other ways you can test your A1C, either in a lab or at home.

How to Calculate A1C: 4 Ways 

Using Your Average Glucose Value From a CGM

Most CGMs can provide you with a 30, 60, or 90-day average of your glucose readings over a chosen period. Using the calculator or conversion formulas that we shared earlier in the article, you can calculate an estimation of your A1C from your blood glucose data collected from a CGM. 

However, be aware that your average glucose readings from a CGM may also require additional calibration or verification with a reference fasting glucose lab value for more accurate baseline or average glucose depiction. 

Some apps, such as the Nutrisense app, will automatically provide you with your average glucose calculation based on your CGM readings. Though, again, you’ll need to ensure that the baseline is verified by a fasting glucose lab value and calibrated to this if needed for best reliability. 

Calculating Your A1C From Your eAG

If you already know your eAG level from a doctor's visit or another blood test, you can calculate your A1C from your average blood glucose reading by using the calculator or formulas above. Remember, however, that this measurement is an estimation and if you find that your value is outside of the normal range, you may want to speak to your doctor to learn more.

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A1C Home Tests

Options for telehealth and remote doctor visits have never been more popular. To meet the demand, many lab tests now have comparable analogs available to consumers. This includes at-home A1C tests, which can be just as accurate as lab tests prescribed by your doctor. 

While many are available at your pharmacy, some are only available to purchase online. Most are affordable, but costs can stack up with frequent testing if your insurance plan doesn’t cover home tests.

The bells and whistles can vary with the cost, so we recommend shopping around to pick what’s best for you and your needs.

A1C Lab Tests

Lab tests are some of the most common ways to get A1C results. There’s the traditional route, with lab work tests prescribed by a doctor, and there are also on-demand lab tests where outside doctors sign off on the tests without direct consultation. 

Wherever you choose to get them, it may be a good idea to go over the results with a dietitian or doctor who knows your medical history. This way, they can advise you with your unique physiology in mind.