Mega backdoor roth contributions

[yatoshura]

I contributed to my employer's 401K account that support mega backdoor roth (Fidelity's in-plan conversion). My W2 form's box 14 showed Other and the contribution amount as AFTAX. 

Should I expect any 1099 or tax related forms for this mega backdoor contribution? Is this the same as my 401K or Traditional IRA contributions?

Does these contributions lower my taxes for 2025 in any way? How to correctly report this contribution?

Thanks.

[dmertz · Accepted solution]

The plan is required to report on Form 1099-R any In-plan Roth Rollovers performed during the year.

A 401(k) is not an IRA.

After-tax contributions to a 401(k) are not reportable on your tax return, except in the section for determining any Retirement Savings Contributions Credit if you qualify for this credit.