Retirement Plans for Physicians: Defined Benefit, 401(k), and Cash Balance Plans

A physician in their peak earning years, often starting a decade or more later than most professionals because of the length of training, faces a specific retirement-planning problem: a standard 401(k) shelters a relatively small fraction of high practice income, and the years available to catch up are fewer than for someone who started saving at 25. A solo 401(k) alone caps out well under six figures a year. Layering a cash balance or defined benefit plan on top can push total tax-deferred contributions well past $300,000 a year for an older, high-earning physician, at the cost of far more plan complexity and, for practices with employees, a real obligation to fund meaningful contributions for staff as well.

What is a solo 401(k), and who actually qualifies for one?

A solo (or “one-participant”) 401(k) is a standard 401(k) plan design available to a business owner with no common-law employees other than a spouse. It’s the simplest and cheapest plan to administer, and for a physician who practices alone with no staff eligible for the plan (independent contractor billing arrangements, or a spouse-only office), it’s often the right starting point before layering anything else on top.

• The elective deferral limit for 2025 is $23,500, plus a $7,500 catch-up for participants age 50 and over, or, under SECURE 2.0’s new enhanced catch-up provision, up to $11,250 for participants ages 60 through 63 specifically.
• On top of the elective deferral, the plan can accept an employer profit-sharing contribution, generally up to 20% of net self-employment income for a sole proprietor or partner, or 25% of W-2 wage for an S-corp shareholder-employee (the structures discussed in our entity structure guide), subject to the overall IRC 415(c) combined limit of $70,000 for 2025 (or $77,500 including catch-up).
• The moment the practice hires an employee who works enough hours to become plan-eligible (generally 1,000 hours in a year under standard eligibility rules, though SECURE 2.0 introduced a long-term part-time employee eligibility rule for certain part-time staff), the solo 401(k) design no longer works as-is; the plan has to either extend coverage to that employee or the practice needs a different plan design entirely.
• A solo 401(k) alone rarely gets a high-earning physician anywhere close to sheltering the income they’d like to shelter; $70,000 (or $77,500) is real money, but for a physician earning $400,000 to $600,000 or more, it’s a small fraction of income, which is exactly the gap a cash balance or defined benefit plan is built to close.

How does a cash balance plan work, and why is it so popular?

A cash balance plan is legally a defined benefit plan, meaning the employer bears the investment risk and funding obligation, but it’s designed to look and communicate like a defined contribution account: each participant has a hypothetical account balance that grows by an annual “pay credit” (an employer contribution, often age-weighted) plus an “interest credit” at a specified rate, regardless of the plan’s actual investment performance.

• The appeal for physicians is that the age-weighted design lets an older owner-physician receive a dramatically larger contribution than a younger employee, because the plan is funding toward a target benefit at retirement age, and there are fewer years left to fund that benefit for someone closer to retirement. A 60-year-old physician-owner might have an allowable contribution north of $250,000 a year, while a 30-year-old staff member in the same plan might be entitled to only a few thousand dollars.
• Cash balance plans require an enrolled actuary to certify the funding calculation annually, and the plan has to be funded based on actuarial assumptions (an assumed interest rate, mortality tables), not simply whatever the practice decides is convenient in a given year. Underfunding or overfunding relative to the actuarial target creates its own correction issues.
• Unlike a 401(k) profit-sharing contribution, which a practice can skip or reduce in a lean year with relatively little consequence, a defined benefit or cash balance plan generally requires the practice to make its funding contribution every year (the actuarially determined minimum) or face excise tax consequences under IRC 4971 for a funding deficiency. This is the single biggest practical difference from a 401(k): a cash balance plan is a multi-year commitment, not a discretionary annual decision, and a practice with volatile income should model at least three to five years of stable cash flow before committing to one.
• Cash balance plans are almost always paired with, not instead of, a 401(k) profit-sharing plan; the two work together, with the 401(k) providing flexibility and the cash balance plan providing the bulk of the additional sheltering capacity for an older, high-earning owner.

When does a traditional defined benefit plan make sense?

A traditional defined benefit plan promises a specific monthly benefit at retirement (often expressed as a percentage of final average compensation times years of service) rather than a hypothetical account balance, and the funding contribution required to support that promised benefit is calculated by an actuary the same way as for a cash balance plan, but the benefit formula and communication style are less intuitive to participants.

• The maximum annual benefit a defined benefit plan can promise is capped under IRC 415(b) at the lesser of a dollar limit ($280,000 for 2025, indexed annually) or 100% of the participant’s average compensation over their highest three consecutive years.
• For a physician closer to retirement age (mid-to-late 50s or older) with a strong, stable income history, a traditional defined benefit plan can support a larger annual funding contribution than a cash balance plan, because the funding target is pegged to that maximum annual benefit rather than a more modest age-weighted pay credit schedule.
• Traditional defined benefit plans are less common than cash balance plans for physician practices specifically because the account-balance-style statement of a cash balance plan is easier for both the physician and any covered staff to understand, and because cash balance plans offer more design flexibility in how the pay credit formula is structured. A traditional DB plan still shows up in solo, no-employee situations where a physician in their late 50s or 60s wants to maximize sheltering in a compressed number of remaining working years.
• Both plan types terminate or freeze with their own set of rules and IRS filing requirements (a Form 5310 determination letter request is common on plan termination), and unwinding a defined benefit plan is materially more involved than simply stopping 401(k) contributions, a real consideration before committing to one and well before any eventual practice sale.

How does plan design change once the practice has employees?

A single-physician practice with no staff has almost total design freedom. The moment a practice has employees eligible for the plan, IRC 401(a)(4) nondiscrimination testing enters the picture, and it fundamentally shapes what the plan can look like.

• Cross-tested (new comparability) plan design is the standard tool for physician practices with staff. Rather than giving every employee the same contribution percentage, the plan groups employees (often “owner physicians” as one group and “staff” as another) and tests whether the resulting contributions, converted to an equivalent benefit accrual rate, pass nondiscrimination testing on that basis rather than on a simple percentage-of-pay basis. This is what allows a 55-year-old owner-physician to receive a contribution rate many multiples higher than a 30-year-old medical assistant while still passing IRS testing, because the age-weighted accrual rates (not the raw dollar percentages) are what’s actually being compared.
• The testing still requires a real, non-trivial contribution to non-owner staff, generally a minimum gateway contribution (commonly 5% to 7.5% of pay, depending on the specific plan design and the owner’s own contribution level) under the cross-tested design rules. A practice can’t design its way out of funding staff altogether; the design just skews the ratio heavily toward the owner relative to a straight pro-rata plan.
• The practical tradeoff physicians weigh: the additional tax-deferred capacity from a cash balance or defined benefit plan has to be measured net of the staff contribution cost, not gross, alongside the other employee benefits staff are entitled to. A practice with a large support staff relative to physician headcount may find the staff cost erodes much of the advantage; a practice with a lean staff-to-physician ratio (common in many specialist and solo practices) usually finds the numbers work strongly in the physician’s favor.
• An enrolled actuary or third-party administrator experienced specifically with medical practices should run the actual testing and contribution modeling before a practice commits, since the math is sensitive to staff age, tenure, and compensation in ways that are difficult to estimate by hand.

How should a physician decide between these options?

Start with the solo 401(k) as the baseline in every case; it’s cheap, flexible, and there’s no reason not to run one even alongside a larger plan. Layer a cash balance plan on top once the practice has stable, predictable income for at least several years running, since the multi-year funding commitment is the real constraint, not the tax math. And if the practice has employees, get an actuarial illustration comparing net owner benefit (after the required staff contribution) before assuming a cash balance plan is worth it purely because the headline sheltering number looks large.

Related guides:

• Medical practice entity structure: PC, PLLC, and S-corp election, since the W-2 wage from an S-corp sets the contribution base for these plans
• Physician compensation models: RVU-based, salary plus bonus, and K-1 income, for how partner compensation interacts with plan contributions
• Employee benefits for medical practices, the broader benefits picture retirement plans sit within
• Selling a medical practice: goodwill and capital gains treatment, for how a terminating retirement plan factors into a practice sale or transition

This guide is general information, not tax advice for your specific situation. Which points apply, and how, depends on your facts.