I did a backdoor roth in 2018 and declared $5,500 on my traditional non-deductable IRA. Do I need to addend? How would I do that? Will I pay more?

[DanielV01]

Did the backdoor include the 5500 contributed to the nondeductible IRA?

[casheverytime1]

Yes, I used the $5,500 from the traditional IRA to convert to a ROTH IRA as a backdoor

[DanielV01]

When did you do the contribution/conversion?  Did you do so in 2018?  If you did, did you receive a 1099-R?  If so, did you include the 1099-R in your original return?

[casheverytime1]

I did the conversion after I filed my taxes.  I haven't received a 1099-R and it's not available with vanguard at this time

[DanielV01 · Accepted solution]

It will be reported next year.  Although your contribution to the nondeductible TIRA can be considered a 2018 contribution, a conversion is reported in the callendar year in which it occurs.  

There is some logic to this.  First, a conversion does not count as contributed funds to a Roth IRA, so this allows you to make a full contribution still in the calendar year.  

Second, a conversion requires documentation.  From a mechanics standpoint, you are withdrawing (receiving a distribution from) your TIRA and immediately transferring it (similar to a rollover, except that the distribution is taxable if it is from a traditional IRA) to your Roth.  Whenever you receive a distribution from an IRA, the activity must be reported (even if it is not taxable), within the callendar year the distribution is received.  

Since your TIRA is nondeductible, you only need to report the contribution now. (Hopefully you did this as part of filing your original return.  If you did not, you will want to amend your return to report the contribution even though you don't pay additional tax on it).  Next year you will report the conversion when you receive the 1099-R indicating the distribution.  

This FAQ explains a conversion in more detail:  https://ttlc.intuit.com/replies/3300628