Medically Reviewed By: Tom Iarocci, MD

If you are a diabetic, then periodically your doctor will give you a test that measures your A1C levels. The number he gives you will be a percentage that represents just how well your blood glucose levels have been controlled with your current regimen. A1C is a very different test from the blood glucose monitoring you do at home. Your A1C reflects your blood glucose levels, on average, over a period of several months, whereas your home blood glucose is more like a snapshot in time.

The A1C Test and A1C/eAG Calculator:

There is a mathematical formula that can be used to convert, or go back and forth, between your finger stick glucose test results and your A1C. You may have heard the term eAG, which means estimated average glucose. eAG helps you approximate what your A1c would be in in terms of the blood glucose levels you are used to reading from your meter, such as 154 mg/dL. In fact, an A1C of 7% corresponds to an eAG of 154 mg/dl.

Calculators are available on a variety of websites. The calculators help you go from eAG to A1c, and vice versa. Once you enter an eAG and click the button, you'll have an approximate A1C value to review that corresponds to that eAG. It is important to note that the A1C results you get from the A1C calculator will not be as accurate as those you get from your doctor, but they will give you a ballpark figure representing how things are going.

The American Diabetes Association explains that eAG is not the same average glucose level as the average of your readings on your meter—that’s because people with diabetes are more likely to check their blood glucose when they are low, such as first thing in the morning before breakfast, so the average of the readings on their meter is likely to be lower than their eAG.

Your regular practice of self-monitoring will be the main guide to show you just how well you're doing on a daily basis. These home readings can tell you which foods are having what type of impact on your sugar levels, how you are responding to medication, and what effect stress or infection might be having on your body. Together, the A1C test and A1C calculator, regular glucose monitoring, and consultations with your doctor will give you the big picture of how you are living with your diabetes.

How Often Should You Be Tested?

Whether you use the calculator to test your A1C monthly or you wait for several months to do it, the American Diabetes Association recommends that your A1C be measured at least twice a year if you are managing well. But for those who are having a difficult time getting their diabetes under control, these tests should be done more frequently, at least every three to four months.

To find out how well you're doing with your diabetes, it is strongly recommended that you have regular visits to your doctor. They will likely prescribe a variety of medications to help you control your blood glucose levels, but it is up to you to keep a regular log of how you're responding and what your blood glucose levels have been doing. That information, including the A1C test and A1C calculator data, in your doctor's hands, is critical to making sure your disease is under control and your treatments are not only right for you, but also the most effective they can be.