Late Contributions to 401k plan

Just curious, if a partner(s) accidentally forgot to make a 401(k) contribution to the plan for 2021 via their Schedule C or K-1 income, can they still make it for 2021 even though it's no longer deductible on the business tax return for the 2021 year?

Did they have a valid election to make a 2021 elective deferral. If so I think you have a late deposit and all that entails but you still need to make it. Timing will determine the year of deduction and 415 limitation year that it is applied to.

If no election you're too late.

They elected to make a 2021 deferral as it was part of the original tax return, just never made

By "business tax return", are you referring to the partnership's tax return? I don't the partner's contribution is deducted on the partnership return; it is deducted on the partner's individual 1040.

On 10/28/2022 at 3:10 PM, ftam said:

if a partner(s) accidentally forgot to make a 401(k) contribution to the plan for 2021 via their Schedule C or K-1 income,

Assuming they made a timely election as your response to Lou S. indicates they did, they would have made the contribution either by the partnership's withholding the amount from year-end or later distributions, or by the partner's writing a check back to the partnership for the amount. In theory, the election created a legal obligation for the partnership to fund the contribution(s) to the plan. The partnership as the plan sponsor needs to make the contribution and then the partner's obligation to the partnership for the cash is a matter determined under the partnership agreement, which probably specially allocates it to the partner. If the individual has enough in their capital account, the partnership could pay the cash to fund the contribution and charge it against the partner's(s') capital account(s). Most partnership agreements would then require that the capital account reduction be made up from available cash distributions going forward or by the partner's writing a check.

On 10/28/2022 at 5:27 PM, ftam said:

They elected to make a 2021 deferral as it was part of the original tax return, just never made

More questions than answers but we need to know the facts. An election is made on a piece of paper or some similar correspondence. The deduction for a partner is taken on the partner's 1040, Schedule 1. Did the partner take the deduction and not make the contribution? Or did they neither take the deduction nor make the contribution? If the latter I would be inclined to just move on.