I've contributed to my grandkids 529 Education accounts for years, and there's probably more than will ever be used. Yet I still contribute to take advantage of NYS's $10K income tax deduction (6.57% marginal tax bracket). I know there's a 10% penalty on earnings for unqualified withdrawals. I figure I can leave the money in the accounts until after I've retired and in a lower tax bracket, but wonder if I should just stop funding and lose the deduction. Any comments?
Of course NYS doesn't tax SS, so let's say that you'll be saving around 2% on the difference in rates between now and when you retire. (NY recaptures the deduction by taxing the past contributions when you make nonqualified withdrawals. See IT-201 Line 22.)
Assuming that the excess contributions earn a cumulative return of at least 20% over the years, the 10% penalty on the earnings will more than wipe out any savings on the NYS side.
Beyond that, what you've got is essentially a non-deductible IRA. The money goes in post-tax (federal), the earnings are sheltered, and then taxed as ordinary income rather than cap gains/qualified divs when withdrawn.
Post-tax contributions can make sense if you're planning to invest in very tax-inefficient funds, like the 529 Income Portfolio. But if you're planning on investing in something more tax-efficient, I don't think that nondeductible contributions pay off.
Here's another way to ask the question: are there readers who would contribute to a nondeductible IRA if they could not convert it to a Roth? If this is not a winner, and if the 10% penalty consumes any benefit you get from the (temporary) NYS tax deduction, then there's not an obvious benefit in making the excess contributions.