I agree with both responders that different people may need the information for different purposes. Going through this exercise, I realized that what most people probably need is a taxpayer's top incremental tax rate, which TurboTax accurately reports as "Tax Bracket", as this must be used to determine the tax effect of any incremental change in income. Examples are decisions involving advancing or deferring income and deductions , or for comparison of taxable vs. tax-exempt bond fund yields - all must be calculated using the top bracket.
The reason that I asked for the definition of Total Tax Liability is that one responder said that it was used in the Effective Tax Rate calculation. On the other hand, using AGI results in a figure that's closer to TurboTax's number, but not always. So there must be some other included value. In my analysis of 6 consecutive returns for the same payer, Total Tax divided by AGI only once resulted in an exact match with the reported Effective Tax Rate; 3 other years had a less than 1% difference, and the remaining two had 3% and 11% differences.
Thanks again all.
