You're far from alone. There's a LOT of room for improvement in TurboTax's support for Form 2210 Schedule AI. It's true that TT doesn't have (all) the necessary info about the timing of various income and expense items, but that does not mean it has to plop as much of the calculation in the lap of the user as it does.
It could, for example, revisit each income and expense item/category that the user entered a value for for the whole year and, whereas before it asked for annual figures, now ask for figures by period. Then it would have everything necessary for the entire calculation. It could also take advantage of the date info that I suspect is included in what it already downloads from financial institutions for things like capital gains, dividends, interest, etc. If I used Quicken, I would be sorely disappointed to find that TT wouldn't even take advantage of the detailed timing info stored in its own sibling product.
The whole point of paying for a product like TurboTax is to avoid having to digest the IRS's publications and complete all the forms yourself. To the extent it doesn't do that, it defeats its purpose. The way it doesn't help annualize Social Security benefits at all is particularly awful given the relative complexity of calculating that one by hand — the taxable portion of it depends on your other income. Currently, if SS income was entered for the year, the annualization Q&A just gives the user an out-of-date reference to an IRS worksheet (that in turn draws on other worksheets), then asks for the per-period AGIs. (There's even a confusing bug in the screen that asks for them, described here.)
I really hope someone can get Form 2210 Schedule AI on the shortlist of areas of the product to fill out next. With the rise of the gig economy, more and more self-employed users are going to have need for that area of the program and as it stands it does not make for a good experience.
