Solo 401(k) for Dentists: 2026 Contribution Limits & Calculator

A solo 401(k) lets a dentist with no full-time employees shelter up to $72,000 in pre-tax income in 2026 — far more than a SEP-IRA at lower income levels. Use the calculator to find your exact maximum based on your practice structure and income.

What Is a Solo 401(k)?

A solo 401(k) — also called a one-participant 401(k), individual 401(k), or self-employed 401(k) — is a standard 401(k) plan that covers a business owner with no full-time W-2 employees other than a spouse. Dentists who own a solo or small practice where they are the only employee (or employ only their spouse) typically qualify.

The solo 401(k) uniquely allows you to contribute in two capacities: as an employee making salary deferrals, and as the employer making profit-sharing contributions. This two-bucket structure is why it outperforms a SEP-IRA at moderate income levels.

2026 Contribution Limits

How the Employer Contribution Calculation Differs by Entity

Sole Proprietor or Single-Member LLC

The employer profit-sharing contribution is calculated as 20% of your net self-employment income (IRS Publication 560 simplified rate — the technically exact calculation adjusts for the 1/2 SE tax deduction, which yields effectively 20% of net income). This contribution is capped at the annual addition limit minus your employee deferral.

Example — solo dentist, age 42, net SE income $200,000:

• Employee deferral: $24,500
• Employer profit sharing: $200,000 × 20% = $40,000
• Total: $64,500
• SEP-IRA (same income): $40,000 — $24,500 less

S-Corp or PLLC

If your practice is an S-corp and pays you a W-2 salary, the employer contribution is 25% of your W-2 salary (not total S-corp distributions). The employee deferral is also limited to your W-2 salary. This is why setting the right salary level matters — too low, and both contributions shrink; too high, and you lose the SE tax savings the S-corp provides. Use our S-corp calculator to find the optimal salary.

Example — S-corp dentist, W-2 $130,000, age 42:

• Employee deferral: $24,500
• Employer profit sharing: $130,000 × 25% = $32,500
• Total: $57,000
• SEP-IRA (same W-2): $32,500 — $24,500 less

Solo 401(k) vs. SEP-IRA: When Each Wins

The SEP-IRA is simpler to administer and has the same employer contribution formula, but it has no employee deferral bucket. That means the solo 401(k) always wins at income levels where the deferral headroom matters:

The advantage is exactly $24,500 (the employee deferral amount) at virtually every income level below the point where the SEP-IRA itself hits the $72,000 cap (~$360K of W-2 compensation for S-corp owners). The breakeven point where both options yield the same $72,000 contribution occurs when employer contribution alone fills the $72,000 bucket — at $288,000 net SE income for sole props ($72,000 ÷ 0.25 = $288K).

Roth Solo 401(k): The Pre-Tax vs. Roth Decision

Most solo 401(k) plans now offer a Roth option. High-earning dentists generally should default to pre-tax contributions — the immediate deduction at 37% is hard to beat. However, Roth makes sense when:

• You're in a lower-income year (new associate, parental leave, partial year)
• You expect significantly higher taxes in retirement (e.g., large practice sale proceeds + Social Security + RMDs)
• You're stacking a cash balance plan that will generate large RMDs later — diversifying with Roth reduces future taxable income

Layer a Cash Balance Plan on Top

Once your practice nets $300,000+ and you're past age 45 or so, the $72,000 solo 401(k) limit often isn't enough to make a meaningful dent in your tax bill. The next step is a cash balance plan layered on top. A 52-year-old dentist netting $500,000 can shelter roughly:

• Solo 401(k): $72,000 (plus $8,000 catch-up = $80,000)
• Cash balance plan contribution: ~$175,000–$200,000 depending on age/actuarial assumptions
• Total pre-tax: $255,000+

Both plans share the same employer contribution pool — the cash balance plan counts against your net SE income available for tax purposes, not against the 415(c) limit. See the cash balance plan guide for age-based contribution tables.

Setting Up a Solo 401(k)

Major brokerage plans (Fidelity, Vanguard, Charles Schwab) offer free solo 401(k) plans with good investment options. The trade-offs:

Deadline: The plan must be established by December 31 of the tax year in which you want to begin contributing. Employee deferrals must be deposited by December 31. Employer profit-sharing contributions can be made up to the business's tax filing deadline including extensions (typically October 15 for S-corps).

Plan assets over $250,000 trigger annual IRS Form 5500-EZ filing. There's no cost to file, but missing the deadline ($250 per day penalty) is a common and avoidable mistake.

Tax Savings Are Only Part of the Picture

The retirement contribution decision doesn't exist in isolation. Before maxing your solo 401(k), a financial advisor who works with dentists will also consider:

• Whether your optimal S-corp W-2 salary and the 25% employer match formula interact with SE tax savings
• Whether adding a cash balance plan makes more actuarial sense than pushing your 401(k) to the limit
• Whether your student loan strategy (IBR income-based plans consider AGI) benefits from maximizing pre-tax retirement contributions to lower reported income
• The tradeoff between pre-tax deferrals now vs. Roth contributions given your expected practice sale proceeds and post-sale income