403(b) vs 401(k): What Actually Differs (and What Doesn't)

Same tax treatment, same deferral limit, different employer universe. A 403(b) is offered by 501(c)(3) nonprofits, public schools, hospitals, universities, and churches. A 401(k) is offered by everyone else, generally for-profit employers.

One piece of history explains most 403(b) complaints: these plans grew out of annuity contracts originally designed for teachers, which is why many 403(b) menus still lean annuity-heavy today.

Here is the honest part most comparison articles skip: a 403(b) and a 401(k) are identical on nearly everything that determines your tax bill.

• Employee elective deferral limit: $24,500 in 2026
• Age 50+ catch-up: $8,000, or $11,250 for ages 60-63 under SECURE 2.0's enhanced catch-up
• Roth option availability (plan-dependent in both)
• Pre-tax contribution treatment for traditional deferrals
• Early-withdrawal treatment: a 10% additional tax generally applies before age 59.5, with the same standard exceptions
• Required Minimum Distribution treatment, including the SECURE 2.0 elimination of lifetime RMDs on designated Roth accounts starting in 2024
• Loan availability, which is plan-dependent in both plan types

Here is the mistake people actually make: they burn hours researching "which is better" when they cannot choose between them anyway. Your employer type decides that for you. The useful question is not which plan wins, it is what to do with the one you already have.

Difference 1, the investment menu. A 403(b) can be limited to annuity contracts under IRC 403(b)(1) or custodial mutual fund accounts under IRC 403(b)(7), and many carry high-fee annuity products, especially in K-12 plans. A 401(k) typically offers a broader fund lineup. This is the fee difference, and fees compound for thirty years.

Difference 2, ERISA coverage. Most 401(k) plans are ERISA plans. Many governmental and church 403(b) plans, and some non-electing employer 403(b) plans, are exempt from ERISA. In plain terms: ERISA coverage brings fiduciary oversight of your plan's investments and strong federal creditor protection. A non-ERISA plan leans on state law instead. For a physician worried about a lawsuit, that is not an academic distinction, it is the difference between a federally shielded account and one that depends on where you live.

Difference 3, the aggregation rule when you have two plans. This is the one that costs people real planning room, and it gets the full treatment below.

The one contribution difference in the 403(b)'s favor: employees with 15 or more years of service at a qualifying employer, such as hospitals, schools, home health agencies, and certain church-related organizations, may be able to defer extra above the standard limit, subject to a lifetime cap and a use-it formula under IRC 402(g)(7).

Who realistically uses it: long-tenure hospital and university employees, career teachers. Most physicians who job-hop between residency, fellowship, and their first attending position will never qualify, since the clock resets with the employer, not the profession.

The highest-value reader on this page is the hospital-employed physician with 1099 moonlighting income who opens a solo 401(k) for that side income. This is the section every ranking article gets wrong, or skips entirely.

Two layered limits govern this. First, one shared employee deferral limit applies across all your plans combined: $24,500 total in 2026, not $24,500 per plan. Second, a separate overall annual-additions limit applies per plan or employer, the IRC 415(c) limit, currently $72,000.

Here is the counterintuitive core, and it is confirmed against the IRS's own guidance, not a blog theory. For two genuinely unrelated employers, each sponsoring a 401(a)-type plan, including a 401(k), the 415(c) limit applies separately to each plan. That is the well-known "double-dip": a hospital 401(k) job plus your own solo 401(k) each get their own full $72,000 room. A 403(b) is treated differently. Because a 403(b) annuity contract is legally deemed to be controlled by the participant, not the employer, for this specific purpose, IRC 415(k)(4) requires the participant's 403(b) contributions to be aggregated with contributions to any retirement plan the participant separately controls through their own business, such as a solo 401(k) funded by moonlighting income. In practice: a hospital-employed physician's 403(b) and their own solo 401(k) share ONE combined 415(c) limit, unlike the same physician with a hospital 401(k), whose two plans each get fully separate room.

Stated plainly: the moonlighting doctor with a hospital 401(k) has more total theoretical contribution ceiling than the identical doctor with a hospital 403(b). Almost no ranking article says this.

One nuance worth naming so you do not overcorrect: a 401(a) plan from the SAME employer does NOT aggregate with that same employer's own 403(b). The IRS confirms physicians affiliated with tax-exempt hospitals can receive full 415(c) allocations under both the hospital's 401(a) plan and its 403(b) plan. The aggregation exposure is specifically with plans the participant controls through their own outside business, not with other plans the employer sponsors.

One honest caveat before the math: as a practical matter, this rule often does not bind. Even generous employer 403(b) contributions for a highly compensated professional with a side hustle frequently do not add up to the full 415(c) ceiling. The trap mostly matters for physicians with large employer 403(b) or 401(a) contributions stacked against meaningful moonlighting income. It is a rule worth checking, not a guaranteed five-figure loss for everyone.

If you are new to the moonlighting-plus-W-2 setup entirely, our locum tenens and 1099 physician tax guide is the starting point before you get into plan-stacking mechanics.

Stop asking "which plan type is better" and start asking "who controls the menu and the fees." A great 403(b) with index funds at a 0.05% expense ratio beats a bad 401(k) at 1.5% all-in cost, and vice versa. The plan type on your paycheck tells you almost nothing about the quality of what you are actually invested in.

A three-step menu audit you can do tonight:

1. Find the all-in expense ratio of what you currently own.
2. Find the cheapest broad index option available on your plan's menu.
3. Check for surrender charges if your money sits inside an annuity product.

The plan document is the asset. The account itself is just the wrapper. You control your contribution rate, your investment selection within whatever menu you are handed, and what you build OUTSIDE the employer plan entirely, including a solo 401(k) from side income or a mega backdoor Roth, if your plan allows after-tax contributions.

Some hospital and university employers stack more than one plan type. A 401(a) plan is an employer-contribution plan that commonly sits NEXT TO a 403(b). A 457(b) plan, where offered, has its own entirely separate deferral limit that does not share the 402(g) limit with a 403(b) or 401(k).

We do not own those two comparisons on this page. If a 401(a) is your actual question, see 401(a) vs 401(k). If the question is whether to fund the 403(b) or an IRA first, see 403(b) vs Roth IRA.

One sentence on the upside: a hospital offering a 403(b), a 401(a), and a 457(b) together can shelter far more income than a single 401(k) ever could. That stack is exactly the kind of planning conversation worth having before you assume your options are limited.

This is not a "which to choose" section, because you cannot choose. It is a "what to do" sequence, in order.

Step 3 is its own full decision with its own math; we do not re-teach it here. See Roth vs traditional 401(k) decision for the worked bracket comparison, which applies identically whether your plan is a 403(b) or a 401(k). Step 4 gets its full treatment in how a solo 401(k) works for 1099 income. Step 5 is covered in our mega backdoor Roth guide.

This page is for hospital, university, and nonprofit employees, physicians especially, who want to know whether their 403(b) is a handicap. It is also for anyone with BOTH a 403(b) and side income considering a solo 401(k), and for job-changers moving between nonprofit and for-profit employers.

The moonlighting 1099 physician is the reader this page was effectively written for. The two-plan section above is your section.

You do NOT need this page if you have a single 401(k), no side income, and no nonprofit job offer on the table. Your plan choice is already made, and the useful reading is Roth vs traditional 401(k) decision instead. And if you are self-employed with no W-2 plan at all, skip straight to SEP IRA vs solo 401(k).