Can You Contribute to a 401(k) After Year End?

If you are a W-2 employee, you cannot keep contributing to a 401(k) after year end: every dollar you defer has to come out of a paycheck dated on or before December 31. Self-employed savers with a solo 401(k) get more room, and employer matching or profit-sharing dollars follow the business’s tax-return deadline, which often runs months into the new year. The rules below sort out who has time left and who does not.

W-2 Employees: The December 31 Payroll Cutoff

Your 401(k) contributions are salary deferrals, which means they can only be funded by payroll withholding. Once your employer processes the last paycheck of the calendar year, the window is closed. You cannot write a personal check, wire money from your bank, or transfer funds in January to top off the prior year. That is a difference from an IRA, which accepts contributions up to the April tax-filing deadline.¹

The rule is the same for traditional pre-tax deferrals and designated Roth 401(k) contributions. If you want to raise your contribution rate to hit the annual limit, contact HR or your benefits administrator by early December so the change reaches your final pay cycle. Once that check is cut, the only after-year-end activity available to most W-2 employees is correcting an over-contribution.

Solo 401(k) Owners: Two Deadlines, Not One

A solo 401(k) has an employee side and an employer side, and each side has its own deadline.

Employee Deferrals

For an existing plan, the deferral election should be in place by December 31, the same as for W-2 workers. There is one significant exception. Under Section 317 of the SECURE 2.0 Act, an unincorporated business owner — a sole proprietor or single-member LLC — who is setting up a brand-new solo 401(k) can establish the plan and make retroactive elective deferrals for the prior tax year. The deadline for those retroactive deferrals is your individual tax-return due date, not including extensions, which is typically April 15.² If your business is a corporation, deferrals still have to be made within the same tax year.

Employer Profit-Sharing Contributions

The employer side is where after-year-end funding really opens up, regardless of entity type. A self-employed owner can contribute up to 25% of net self-employment income (after deducting the employer-equivalent portion of self-employment tax) as a profit-sharing contribution, and that contribution can go in any time up to the tax-return filing deadline, including extensions.³ For a sole proprietor who files an extension, that pushes the deposit deadline to October 15.

The combined employee and employer total still has to stay inside the Section 415(c) limit of $72,000 for 2026, plus any applicable catch-up amount.⁴ The upside is real: you can calculate your actual net income first and then decide how much to put in.

Employer Matching and Profit Sharing in a Workplace Plan

If you participate in a traditional employer-sponsored 401(k), matching contributions and profit-sharing allocations follow the company’s tax-return deadline, not the calendar year. A business can deposit those funds and take the deduction for the prior year as long as the payment is made by the filing due date, including any valid extension.⁵

The exact date depends on the employer’s entity type:

S-corporations file Form 1120-S by March 15 for calendar-year filers, with a six-month extension available to September 15.⁶
C-corporations file Form 1120 by April 15 for calendar-year filers, with a six-month extension to October 15.⁶
Sole proprietorships and partnerships follow the individual or partnership return schedule, with extensions potentially reaching September or October.

As a participant, you do not control when your employer funds the match. Seeing the deposit land months after year end is normal. Some plans fund each pay period; others make a single lump-sum contribution after finalizing annual calculations.

Fixing an Over-Contribution After Year End

If you deferred more than the annual limit across one or more 401(k) plans, you need to pull the excess out. This happens most often to people who changed jobs mid-year and contributed to two employers’ plans without adding up the total.

There are two steps. Notify each affected plan by March 1 of the following year, telling the administrator how much of the excess to return from that plan. The plan then has to distribute the excess deferrals, along with any earnings on those funds, no later than April 15.⁷

If the correction happens by April 15, the returned amount is taxable income in the year you deferred it and any earnings are taxed in the year distributed, but you avoid being taxed on the same dollars twice.⁸ Miss that April 15 deadline and the excess gets taxed twice: once in the year of contribution and again when it eventually comes out of the plan. The administrator issues a Form 1099-R for the corrective distribution.⁹

2026 Contribution Limits

To know whether you are at, under, or over the line, these are the numbers for 2026. The elective deferral limit is $24,500, up from $23,500 in 2025.¹⁰ Participants who are 50 or older during the year can defer an additional $8,000 catch-up, for a total employee limit of $32,500.¹¹

SECURE 2.0 created an enhanced catch-up for ages 60 through 63. For 2026, that enhanced catch-up is $11,250 instead of $8,000, which raises the maximum employee deferral for someone in that age band to $35,750.¹¹ At 64 you drop back to the standard $8,000 catch-up.

Employee deferrals plus employer contributions together cannot exceed the Section 415(c) limit of $72,000, or $80,000 with the standard catch-up, or $83,250 with the age 60–63 catch-up, since catch-ups sit on top of that cap.⁴

1
Internal Revenue Service. Publication 590-A (2025), Contributions to Individual Retirement Arrangements (IRAs)
2
Charles Schwab. Individual 401(k) Plans – Self-Employed 401(k) Options
3
Office of the Law Revision Counsel. 26 USC 404 – Deduction for Contributions of an Employer to an Employees Trust
4
Internal Revenue Service. COLA Increases for Dollar Limitations on Benefits and Contributions
5
Internal Revenue Service. 401(k) Plan Fix-It Guide – You Haven’t Timely Deposited Employee Elective Deferrals – Section: Timing of Other Contributions
6
Internal Revenue Service. Publication 509 (2026), Tax Calendars
7
Office of the Law Revision Counsel. 26 USC 402 – Taxability of Beneficiary of Employees Trust
8
Internal Revenue Service. Consequences to a Participant Who Makes Excess Deferrals to a 401(k) Plan
9
IRS. Corrective Distribution of Excess Contributions
10
Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500
11
Internal Revenue Service. Retirement Topics – 401(k) and Profit-Sharing Plan Contribution Limits