Briefly, recharacterization of a Roth conversion is (used to be) useful if you wanted to undo a Roth conversion sometime before your tax return is filed for the year in question. If you’d like more information on recharacterization and why you might want (or have wanted) to do this, you can check out the article on Recharacterizing.
So now, if you convert funds from an IRA or 401k into a Roth IRA account, you no longer have this back-out option available to you.
The legislation did not make it clear whether the restriction takes place for any recharacterization after 2017 or if it’s based on any conversion done after 2017. This makes it unclear whether a 2017 conversion could still be recharacterized by October 15, 2018, or if the recharacterization had to be complete by year-end 2017. The verbiage used indicates that the recharacterization disallowance “shall apply to taxable years beginning after December 31, 2017.”
Some think this means the ban applies to conversions after 2017 – while others think this means the ban applies to recharacterizations after 2017. Jury is still out on this, and IRS is likely to clarify later this year.
jb note: Astute super-reader clydewolf mentions:
Kaye Thomas at Fairmark.com says he has confirmed with the IRS
that 2017 Conversions can be recharacterized.
http://fairmark.com/forum/read.php?2,84769
Other types of recharacterization are still allowed – the primary one being recharacterizing of an unintended IRA rollover or contribution that is later disallowed due to income limitations. This type of recharacterization is still allowed after TCJA 2017.
For example, if you contribute the maximum amount ($5,500) to your IRA this year and later you discover that your income is above the limits for a deductible IRA contribution (but still under the Roth IRA contribution limits). You have the option of recharacterizing the contribution in your traditional IRA to a Roth IRA contribution. With this action, your recharacterized contribution will be treated as if made to the Roth IRA at the same time as you originally made it to the traditional IRA – as long as you recharacterize before the filing date of your tax return (generally October 15 of the following year after the contribution).