I’m thinking of converting my traditional IRA to a Roth IRA. What’s the deadline for doing this?

While annual contributions to Roth IRAs can be made up to the due date of the return (e.g., April 15, 2019, for 2018 contributions), a Roth IRA conversion is taxable in the year it is made. So if you want to report the income from the conversion in 2018, the conversion must be completed by December 31, 2018. Keep in mind that you cannot undo a 2018 conversion (as was possible in the past); conversions in 2018 and beyond are permanent.