Profit sharing plans: flexible employer contributions once you have staff

Primary sources: IRC §401(a); IRC §404(a)(3); Treas. Reg. §1.401(a)(4) (new comparability testing)

The short answer

A Solo 401(k) works when it's just you. Once a business has employees, a profit sharing plan — usually layered on top of a 401(k) as one combined plan — is how an owner keeps making large, tax-deductible employer contributions while deciding year to year, discretionarily, how much to contribute and, with the right plan design, skewing more of it toward themselves through "new comparability" allocation formulas. Contributions are deductible to the business, grow tax-deferred for participants, and the plan can be funded generously in good years and scaled back or skipped in lean ones — unlike a cash balance plan's mandatory funding.

Who this works for — and who it doesn't

Good fit

Businesses with W-2 employees who want retirement plan flexibility without a rigid annual funding requirement
Owners significantly older or higher-paid than staff, where new comparability design can allocate more to the owner
Businesses layering this on top of an existing 401(k) for extra deductible capacity

Not a fit

Solo owners with no employees — a Solo 401(k) alone is simpler and usually sufficient
Businesses wanting a guaranteed, predictable large deduction every year — a cash balance plan fits that better
Very small staffs where testing and administration costs outweigh the flexibility gained

How it works

The plan is typically paired with a 401(k) as a single combined document, so employees can also defer their own salary.
Each year, the business decides whether and how much to contribute — up to statutory limits per participant — with no fixed obligation like a defined benefit plan carries.
Allocation formulas vary. A pro-rata formula splits contributions by compensation percentage across everyone; a "new comparability" (cross-tested) formula can allocate materially more to owners and key employees within nondiscrimination limits, when the demographics support it.
Vesting schedules can be set so employees earn full ownership of employer contributions gradually, encouraging retention.
Contributions are deducted by the business in the year made, subject to the overall deduction limit tied to compensation.

A worked example

A 6-person agency owner, age 52, wants to maximize her own retirement contribution while keeping staff costs reasonable.

Illustrative profit sharing allocation

Owner's 401(k) deferral + catch-up$31,000

Owner's profit sharing allocation (new comparability design)$39,500

Required contributions for 5 staff (gateway minimum)$16,000

Total deductible plan contribution$86,500

Illustrative only — actual allocation depends on age and compensation demographics across the whole staff and must pass nondiscrimination testing each year.

Common mistakes

New comparability designs live or die on the census. A plan modeled on last year's staff can fail testing the moment headcount or ages shift — run it every year, not once at setup.

Assuming a favorable allocation formula from year one will keep passing testing automatically as staff changes
Treating the "discretionary" contribution as truly optional without budgeting for the required minimum gateway contribution to staff
Not coordinating the plan design with a 401(k) safe harbor election, which can simplify testing considerably
Ignoring vesting schedule design, which affects both cost and retention incentives

Have employees and want more deductible retirement capacity?

We'll model a new comparability allocation against your actual staff census before you commit to a plan design.

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