Maybe there is, as you say, “no standard or official definition”. But a quick look at definitions around the internet for the term "Effective Tax Rate" reveals that this term generally refers to: TOTAL TAX / TAXABLE INCOME, expressed as a percentage. The only variations to this look more like the result of being poorly researched and/or written by the authors.
Turbo Tax's hijacking of a term that once had clear meaning is not just at odds with what 'I' understood the term to generally mean, but it is also at odds with the majority of readily-available definitions; at least for common preparers of our own taxes. From where do you find other variative definitions of this term that are as widely used and accepted as the definition above (TOTAL TAX / TAXABLE INCOME)?
For 2023, Turbo Tax says my Effective Tax Rate is 14.04%. TOTAL TAX / TAXABLE INCOME percentage calculates to 20.0% which is nearly 6 points higher than what Turbo Tax says. And TOTAL TAX / ADJUSTABLE GROSS INCOME gives 17.3%; which is about 3.3 points higher.
So, this stuff is all over the place, and without any kind of useful accompanying definition is misleading. Turbo Tax should either get rid of their imposter ETR, or rename it and define exactly what it is supposed to be.
