If your employer made the excess contributions, they might already be included in your gross income. If this is the case, you don’t need to do anything extra.
But if the excess contribution isn’t included in box 1 of Form W-2, you’ll need to report the excess in the “Other income” section of your tax return.
In addition, you must pay a 6% excise tax on excess contributions. See Form 5329, Additional Taxes on Qualified Plans (Including IRAs) and Other Tax-Favored Accounts, to figure the excise tax. The excise tax applies to each tax year the excess contribution remains in the account.