Does an excess deferral is 2018 get reported and corrected on 2018 tax return or 2019 return?

2018, however if there were earnings that were returned in 2019, the earnings are reported on a 2019 tax return, the returned contribution on the 2018 tax return.   Code P reported on 2018, code 8 in 2019.

The code 8 is for taxable earning received in 2018 that are reported on your 2018 tax return.

The code P is the return of 2017 excess that must be include  as 2017 wages on an amended 2017 tax return.

Amended returns can only be mailed. It is suggested that it be mailed certified with return receipt (or other tracking service) to verify that the IRS receives it.


https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed

https://ttlc.intuit.com/replies/3288565

You can check the status of the amended return here, but allow 3 weeks after mailing.

https://www.irs.gov/filing/individuals/amended-returns-form-1040-x-/wheres-my-amended-return-1