Employee deferral contributions
Pass-through entities (sole proprietors, partnerships, LLCs not taxed as corporations): Employee deferral contributions may be made up to the tax filing deadline of the business, including extensions; either September 15 or October 15.
W-2 / corporate environments (S corporations, C corporations): Employee contributions are tied to payroll and must be deposited within a short period after each pay period. Your final opportunity to make employee deferrals for the tax year is your last payroll run, generally processed by December 31, with funds typically deposited in early January.
Employer profit-sharing contributions
Employer profit-sharing contributions may be made up to the tax filing deadline of the business, including extensions, regardless of business structure.
- S Corporations, Partnerships, and LLC's electing S Corporation status: typically September 15
- Sole proprietorships, Single member LLCs, and C Corporations: typically October 15
When a deadline falls on a weekend or holiday
If a contribution deadline falls on a Saturday, Sunday, or federal holiday, the deadline shifts to the next business day.
A note on timing
Deadlines for Solo 401(k) contributions can interact with your overall tax return preparation. Confirm your contribution amounts and deadlines with your tax advisor before filing, particularly in years where you are making catch-up contributions or changing your contribution approach.
Frequently Asked Questions
Can I make employee deferral contributions after December 31 if I'm in a pass-through entity? Yes. In a pass-through environment, there is no payroll event to which contributions are formally linked. You determine your income when you file your taxes, so employee deferrals can be made up to your business tax filing deadline including extensions.
What if I miss the final payroll deadline for my W-2 employee contributions? If you operate through a corporation and miss the final payroll of the year, you will be unable to make employee deferral contributions for that tax year. Employer profit-sharing contributions remain available until the corporate tax filing deadline including extensions.