Contributing to a 401k for previous years

[question123432]

My employer failed to contribute to my 401k for multiple years.  I had money taken out of my checks in 2024 (so they would match it) to make up for what should have been taken out all along.  I received my W2 with the amounts and corresponding years for those amounts, but there is no way to enter that on my tax form.  How can I specify the amounts are for different years? 

[DavidD66]

If I understand your question, your employer did not withhold 401(k) contributions from your pay in previous years.  In 2024, your employer did withhold 401(k) contributions.  The amount you had withheld in 2024 included the amounts that should have been withheld in previous years, but wasn't.  Your W-2 shows your 401(k) withholding by year on your W-2 and your employer made a matching contribution in 2024 for the current year and the previous years when nothing was withheld.  If that is correct, you don't need to do anything other than report the total amount of 401(k) withholding reported on your W-2.  There is no way, and no reason to identify it by the year it should have been withheld because it wasn't.  There won't be any problem as long as your total 401(k) withholding is not more than the contribution limit of $23,000 for 2024.  If you're age 50 or older, the additional $7,500 in catch-up contributions, would raise your employee deferral limit to $30,500.