solo 401k redesignation

[DavidS]

Summarized: Can a contribution made in 2023 designated for 2022 be changed to a 2023 designation?
Detail: Using a client's 2022 P&L and balance sheet I calculated his tentative tax liability and tentative solo 401k contribution amounts. He then made that contribution in March of 2023. When it came time to finish his tax return he informed me an asset purchase made in 2022 that reduced his self employment income to zero. Now he has an excess deferral. Can that contribution be redesignated to a 2023 contribution. Thanks for your help.

[Rapid Robert]

Pub 560 has your answer:

"If you contribute more to a plan than you can deduct for the year, you can carry over and deduct the difference in later years, combined with your contributions for those years. Your combined deduction in a later year is limited to 25% of the participating employees' compensation for that year. [...] The amount you carry over and deduct may be subject to the excise tax discussed next."