The earnings on the excess contribution made in 2018 but withdrawn in 2019 are reportable as income in the year you made the excess contribution, i.e., 2018.
Because you made the withdrawal of the excess contribution before the due date of your 2018 tax return, you will not be subject to the 6% tax on excess contributions.
As long as you did not deduct the excess withdrawal in 2018, you do not have to report the excess withdrawal amount in your income.
Click here for the section of IRS Publication 590A pertaining to excess contributions and the associated earnings.
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