Are losses on a roth ira tax deductible for the 2018 tax year per the new tax code?

[MichaelDC]

Yes, but it's been deductible for a while. Be careful in that it's an itemized deduction and subject to the 2% of AGI limit. To qualify for the deduction, you must close all of your Roth IRA accounts, including Roth IRA accounts that have profits. 

Your traditional IRAs need not be closed, as they are treated separately, and the value of your Roth IRA from the previous year or at any point during the time the account was open does not matter. You must show a loss from your tax basis in the account.

Your deduction is equal to the amount by which your tax basis exceeds your total withdrawals from your Roth IRAs. Your tax basis is the total amount of your contributions to the Roth IRA because these contributions are made with after-tax dollars.

For example, if over the years you have contributed $25,000 to your Roth IRA but receive $15,000 when you close the account, you would have a net loss of $10,000.

If you have any other details regarding this question, please feel free to post them in the comment section. 

[dcfagerlie]

Along those lines then, if roth loss is 14000 - two per cent less is 12040 does that mean I can harvest 12040 of gains in my regular brokerage account to offset the loss

[MichaelDC]

The 2% of the AGI rule example: if your AGI is $100,000 and your loss is $14K, then $2k of the loss won't help and the remaining $12k will be the "actual" deduction. This example would be the equivalent of a $12k donation.

[dcfagerlie]

So the 12000 loss in the roth can or cannot be used to offset gains from a different brokerage account... to the extent of the full 12000

[MichaelDC]

In a sense it does, but by way of Schedule A along with mortgage interest, taxes, donations and work expenses.

[dmertz]

2017 is that last year for the deduction described above.  For 2018 and beyond, miscellaneous deductions subject to the 2% of AGI floor have been eliminated, so the deduction for unrecoverable traditional or Roth IRA basis has been eliminated with it.