How does Turbotax calculate the average tax rate displayed in the graphical summary page?

[Western403]

On the Summary Graphical page, when I divide the Taxable Income by the Tax Payable, I get an average tax rate which is consistently higher by a few percent than the Average Tax rate listed below on the summary graphical page.

I have checked and found this apparent discrepancy in various tax returns and in various tax years (2023,2022, 2021). Is this an error or what am I missing in the calculation?   

[TurboTaxSusan]

Please contact our phone support team at 1-888-829-8608 as they will be better able to assist you.

[Western403]

I spent 30 minutes trying to navigate through the obtuse voice recognition / routing system to finally reach an in-person agent who didn't have any answer, then got put on hold, and after waiting through 10 minutes of muzak, I finally got the response that no one more knowledgeable was available, and to "have a wonderful day".

I give up.