How to declare 2018 Excess Contributions Discovered in 2020?

[jeremy10]

In 2020 I discovered that in 2018 I made excess contributions to my traditional IRA. Do I declare this mistake (and pay the penalty) when filing my 2019 or 2020 taxes?

Since I will be receiving the 1099-R for the removal of the excess distributions for my 2020 taxes I know that I will need to file Form 5329 with my 2020 taxes. Do I need to amend my 2018 taxes to include Form 5329 and should I file a form 5329 with my 2019 taxes?

[MinhT1]

As the excess contribution to your Traditional IRA, you'll need to amend your 2018 tax return to report the excess contribution and calculate the taxes on form 5329.

Likewise, as the excess was not withdrawn in 2019, you'll need to file form 5329 with your 2019 tax return and pay the 6% excise tax.