Can I roll unused 529 money into a Roth IRA, and what are the rules?

Yes. Since 2024, you can roll leftover 529 funds into a Roth IRA for the same beneficiary, up to a $35,000 lifetime maximum. This solves the old worry that over-saving meant penalties. The rules are strict: the 529 must have been open for at least 15 years; you can't roll over contributions (or their earnings) made in the last 5 years; each year's rollover is capped at the annual IRA contribution limit ($7,000 for 2025); and the beneficiary must have earned income at least equal to the amount rolled. The rollover isn't subject to Roth income limits, which is a nice perk. It's a clean way to convert a head start on college into a head start on retirement. Spread the $35,000 over several years to stay within annual caps.