Okay, I think I've figured out what's going on by looking at the form behind that particular "EasyStep" (page of TurboTax's Q&A interface) and consulting the IRS's instructions for that form.
Bottom line up-front:
Check whether that strange uneditable value shown for the whole year is actually 92.35% of the value you expect it to be ("Business income or (loss)" on 1040 Schedule 1, or the total of the "Net profit or (loss)" lines from all your Sch. C's). If it is, then most likely TurboTax still has a bug. Just fill in the first three boxes as if the fourth value were what you expected it to be. That is, fill the first three boxes with what your "business income or loss" was/would-have-been-calculated-to-be at the end of each of the three partial years. If, however, the full year value is NOT 92.35% of what you expect it to be, then you probably have some other inconsistency going on. Make sure you're including in your figuring for the annualization periods the same set of income and expense streams that you earlier entered into TurboTax for the whole year—that you haven't forgotten any.
The details (as of March 15, 2020):
The numbers you put into the boxes for the first three periods go directly into TurboTax's "Annualized Self-Employment Tax Smart Worksheet" behind the scenes. Each of them is then multiplied by 92.35% and put into the "Net earnings from self-employment for the period" line (line 28, as of 2020) of the IRS's Form 2210 Schedule AI. According to the IRS's instructions for that line, that's generally what should go on that line. TurboTax pre-populates the fourth column of that line with 92.35% of your "business income or loss" from 1040 Sch. 1. TurboTax's intermediary "smart worksheet" I mentioned doesn't have a spot for the full year's value, though, and whomever coded that particular EasyStep appears to have linked the full year value displayed in the prompt directly to Sch. AI line 28 column 4. The number on that form should be divided by 92.35% before displaying it to the user (in order to make it comparable to the numbers the user is supposed to enter) but that isn't being done.
Hope this helps someone else (and that TurboTax puts the time into greatly improving the EasySteps for income annualization soon!)
