If you are unable to have your excess 401(K) Contribution refunded by 4/15/19, it will be taxed twice.....once on your 2018 Tax Return and then again in the future when you withdraw the funds. Check out IRS Pub 525 for more details: https://www.irs.gov/pub/irs-pdf/p525.pdf.
You should report the excess contributions to your 401(K) as Wages on line 1 of your 2018 Tax Return by following these steps:
- Click on the "Federal Taxes" Tab
- Click on the "Wages & Income" Tab
- Click on "I'll choose what I work on"
- Scroll down to "Less Common Income"
- Select "Miscellaneous Income" and click Start or Update
- Select "Other income not already reported on a Form W-2 or Form 1099" and click on Start
- Answer the Question "Did you receive any other wages? Yes
- Click through the questions until you get to "Any Other Earned Income"
- Answer Yes to "Did you earn any other wages?
- Indicate "Other" as Source of Other Earned Income and click Continue
- For the description enter "8Excess 401K Deferrals" and click on Done
