Using an HbA1c Calculator

Before my visit to my endocrinologist earlier this week, I was desperately looking for confirmation that I really did take the best care of myself that I possibly could have. I felt like I did, but I needed this to reflect on my A1C directly.

Since an A1C test can determine the average blood glucose levels over a period of approx. three months, I knew that by finding out what my average blood sugar was I could calculate what I to expect for an A1c result at my appointment.

In case you don’t know exactly what the HbA1c blood test measures, here’s a great example from NIH.

How does the A1C test work?

The A1C test is based on the attachment of glucose to hemoglobin, the protein in red blood cells that carries oxygen. In the body, red blood cells are constantly forming and dying, but typically they live for about 3 months. Thus, the A1C test reflects the average of a person’s blood glucose levels over the past 3 months. The A1C test result is reported as a percentage. The higher the percentage, the higher a person’s blood glucose levels have been. A normal A1C level is below 5.7 percent.

So here’s the tool that I found that will help determine a realistic A1C result based on average blood sugars – which can be retrieved from your meter, CGM, or pump (explained below).


First, determine what your average blood sugar is, then enter it on the left. Click calculate and it will generate an A1C percentage. To calculate your own click here to visit the website.

To find your average blood sugar, check on your meter or pump. Under your summaries/logbook area, this should be listed. Here’s what it looks like on my pump:


My last A1C (three days ago), was 6.5%. Because I got a new pump at the very end of December, I only had about 1.5 months of data to work with, which could explain the .3% difference, however small it is.

Have you used an A1C calculator before? Do you find it to be accurate or not?






  1. This is great! Thanks for posting. According to my calculations, I should be sitting at around 6.2%!! My DE is going to lose her mind! At my last appointment it was 7.9%, that was pre Libre.

    Liked by 1 person

      1. I’ll keep you posted. Next appointment 6th of March. Actually looking forward to it for once. My control has been amazing (even if I do say so myself) since Libre.

        Liked by 1 person

  2. The mySugr app has a built in A1C calculator, which I find pretty useful so far! But I also keep in mind that 1) because I can’t log my values 24/7 (fingerpricks) it’s an estimation at best and 2) A1C isn’t necessarily a reflection on how good my control is. A lot of things can affect it over the course of 3 months, including illness. Something about the chemistry of the hemoglobin and glucose when you’re sick, menstruation etc. have influence on the A1C sometimes.

    There are tons of people with poor overall control with low A1C, so I tend to take it with a grain of salt. 🙂 That said, the calculator gives a good average estimate if you can take those factors into consideration, and being able to compare results has its definite uses.


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