Summary: At first, New York TurboTax correctly limited the deduction for a large donation of appreciated stock to 30% of AGI. However, for some reason, it switched to deducting 50% of AGI, which I think is wrong. I can't get it to go back to only deducting 30% of AGI.
Details:
When I filled out my federal taxes, I entered a donation of appreciated stock (valued at the fair market value), which can only be deducted up to 30% of one's AGI per year. Federal TurboTax correctly reported that the deduction amount was only 30% of AGI (and so chose the standard deduction for me instead). When I moved on to NY state taxes, TurboTax also apparently realized that the deduction was limited to 30%.
After finishing state taxes, I logged out. I logged back in again a few days later to keep going on the final steps. I saw that my state tax amount as reported in the box in the top left of the screen was now a lot lower than what I was shown before. I was puzzled but continued along until I got to the final PDF of my federal and state taxes where I could review the calculations. I saw that TurboTax was now trying to itemize my deductions for both federal and state and was claiming the stock donation at 50% of AGI, which is incorrect.
I went back through the deductions section of federal taxes, including the walkthrough about my charitable donation. Then I went through all of state taxes again. In the final PDF of my return, federal taxes were back to just the standard deduction and didn't include the charitable donation. But NY state taxes continued to (I think wrongly) claim a 50%-of-AGI deduction for the stock donation.
I deleted my NY return and redid it from scratch, hoping this would propagate the federal info to state properly, but it didn't work: NY TurboTax was still deducting 50% of AGI from the stock donation.
The New York State Department of Taxation and Finance says on its webpage about itemized deductions that "your New York itemized deduction for gifts to charity is computed using the federal rules that applied to tax year 2023." And IRS's 2023 Publication 526 confirms that the limit is indeed 30% of AGI: "A 30% limit applies to noncash contributions of capital gain property if you figure your deduction using FMV without reduction for appreciation." So I'm pretty sure NY TurboTax should only be deducting up to 30% of AGI, and indeed, that's what it did at first before my tax estimate changed mysteriously.
