There is no retirement plan called a “501k.” When people compare a 501k vs a 401(k), they’re usually mixing up two different parts of the tax code: Section 501(c)(3), which makes an organization tax-exempt, and Section 401(k), which governs a common workplace retirement account. The plan nonprofit employees actually use is a 403(b), and that’s the real comparison worth making. A 403(b) and a 401(k) do the same job, but they differ in who can sponsor them, what you can invest in, and a couple of contribution rules that can matter over a career.
Who Can Offer Each Plan
A 401(k) is for for-profit businesses of any size. The employer sets up a qualified trust to hold the plan’s assets and takes on a fiduciary duty to run it in the participants’ interest.1Office of the Law Revision Counsel. 26 U.S.C. 401 – Qualified Pension, Profit-Sharing, and Stock Bonus Plans
A 403(b) is for a specific list of employers: public schools, nonprofit hospitals, churches, and other organizations tax-exempt under Section 501(c)(3).2Internal Revenue Service. IRC 403(b) Tax-Sheltered Annuity Plans That employer-type restriction is the reason the two plans exist as separate sections of the code. If you work for a hospital that’s part of a for-profit chain, you’ll have a 401(k). If you work for a nonprofit hospital across the street, you’ll have a 403(b).
How the Money Is Taxed and Invested
The tax mechanics are the same. In either plan, contributions come out of your paycheck before federal and state income tax applies, lowering your taxable income now and shifting the tax bill to when you withdraw the money in retirement.3Office of the Law Revision Counsel. 26 U.S. Code 403 – Taxation of Employee Annuities Both plans can also offer a Roth option, where you contribute after-tax dollars and qualified withdrawals come out tax-free, including earnings.
The investment menu is where 403(b) participants often notice a real difference. A 403(b) account can only take one of three forms: an annuity contract from an insurance company, a custodial account holding mutual funds, or a retirement income account for church employees.2Internal Revenue Service. IRC 403(b) Tax-Sheltered Annuity Plans Many plans still lean heavily on annuity products, though mutual fund options have become more common. A typical 401(k) opens the door to a wider range of index funds, bond funds, and target-date funds. If your 403(b) mainly offers annuity contracts, read the fee disclosures closely. Surrender charges and insurance-related expenses can eat into returns in ways a low-cost index fund won’t.
Contribution Limits
The base contribution limits are identical. For 2026, you can defer up to $24,500 of salary into either a 401(k) or a 403(b).4Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500 That cap covers your combined elective deferrals across all plans. If you contribute to both a 401(k) at one job and a 403(b) at another, the combined total still can’t exceed $24,500.5Internal Revenue Service. Retirement Topics – 403(b) Contribution Limits
Age-based catch-up contributions work the same in both plans. At 50 and older, you can add another $8,000, for a total employee limit of $32,500. From age 60 through 63, a “super catch-up” of $11,250 replaces the standard $8,000, pushing the total to $35,750. The higher amount applies only during those four years and drops back to the standard catch-up at 64.4Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500
When employer contributions are added, the total from all sources tops out at $72,000 for 2026, or $80,000 to $83,250 with catch-ups, depending on your age.6Internal Revenue Service. COLA Increases for Dollar Limitations on Benefits and Contributions
The 403(b) 15-Year Rule
Here’s one contribution feature the 403(b) has and the 401(k) doesn’t. If you’ve worked for the same qualifying organization for at least 15 years, you may be able to contribute an extra $3,000 per year on top of the normal limits, up to a $15,000 lifetime cap.7Internal Revenue Service. 403(b) Plans – Catch-Up Contributions This is separate from the age-50 catch-up, so a long-tenured 403(b) participant over 50 could stack both. The 15-year rule uses a detailed calculation that considers your years of service and prior contributions, so the full $3,000 isn’t always available.
The 2026 Roth Catch-Up Rule
Starting in 2026, higher earners lose the choice of where their catch-up contributions go. If your FICA wages exceeded $145,000 (indexed; the threshold for 2026 eligibility is $150,000 in 2025 wages), any catch-up contributions must go into a Roth account rather than a pre-tax account. If your plan doesn’t offer a Roth option, you lose the ability to make catch-up contributions at all until the plan adds one. This rule applies equally to 401(k), 403(b), and governmental 457(b) plans. Workers below the wage threshold can still make catch-ups on either a pre-tax or Roth basis, if the plan supports both.
Vesting and ERISA Coverage
Your own contributions are always 100% vested immediately in either plan. Employer contributions typically follow a vesting schedule. Federal law allows two approaches for individual account plans like a 401(k): cliff vesting, where you go from 0% to 100% ownership after three years of service, or graded vesting, where ownership steps up and reaches 100% after six years.8Office of the Law Revision Counsel. 29 U.S. Code 1053 – Minimum Vesting Standards If you leave before you’re fully vested, you forfeit the unvested employer money.
The Employee Retirement Income Security Act (ERISA) sets the rules for vesting, reporting, and fiduciary duties in private-sector plans. This is one area where 403(b) participants sometimes have less protection than 401(k) participants. Many 403(b) plans sponsored by churches or government entities are exempt from parts of ERISA, which can mean fewer regulatory safeguards.9U.S. Department of Labor. FAQs About Retirement Plans and ERISA Your plan’s Summary Plan Description lays out your specific vesting schedule and rules; ask for it if you don’t have a copy.
Accessing the Money
Loan and withdrawal rules run in parallel across both plans. If your plan permits loans (they’re optional), the maximum you can borrow is the lesser of $50,000 or 50% of your vested balance, with a $10,000 floor when 50% of your balance is below that amount.10Internal Revenue Service. Retirement Plans FAQs Regarding Loans Repayment is usually over five years, with interest going back into your own account.
Hardship withdrawals are available in both plans for a set of qualifying reasons the IRS recognizes as safe harbors, including unreimbursed medical bills, buying a primary home, tuition, preventing eviction or foreclosure, funeral costs, and casualty repairs to your home.11Internal Revenue Service. Retirement Topics – Hardship Distributions Unlike a loan, a hardship withdrawal can’t be paid back and is taxable, plus a 10% early distribution penalty if you’re under 59½.
Once you reach 59½, you can withdraw from either plan without penalty. Regular income tax still applies unless the money came from Roth contributions. Both plans also share the same list of pre-59½ penalty exceptions, including separation from service at 55 or older (50 for public safety employees), qualified birth or adoption distributions, and federally declared disaster distributions.12Internal Revenue Service. Retirement Topics – Exceptions to Tax on Early Distributions
Required Minimum Distributions
Both plans require you to start taking money out at age 73. If you’re still working for the plan’s sponsor at that age, you may be able to delay your RMDs until you actually retire. The first RMD is due by April 1 of the year after you reach 73 or retire, whichever is later; every one after that is due by December 31.13Internal Revenue Service. Retirement Topics – Required Minimum Distributions (RMDs) Missing an RMD triggers a 25% excise tax on the shortfall, dropping to 10% if you correct it within two years.14Internal Revenue Service. Retirement Plan and IRA Required Minimum Distributions FAQs
Rollovers Between the Two
You can roll a 403(b) balance into a 401(k) at a new employer, or the other way around, without owing taxes on the transfer. The mechanics are what matter. Do a direct rollover, where the money moves plan to plan. If you take the check yourself, the plan must withhold 20% for federal taxes, and you have 60 days to deposit the full pre-withholding amount into another qualified account or the withheld portion gets treated as a taxable distribution.15Office of the Law Revision Counsel. 26 U.S.C. 3405 – Special Rules for Pensions, Annuities, and Certain Other Deferred Income
SECURE 2.0 Changes That Hit Both Plans
Two SECURE 2.0 provisions affect 401(k) and 403(b) participants the same way.
Any 401(k) or 403(b) plan set up after December 29, 2022, must automatically enroll eligible employees starting with the 2025 plan year. The initial contribution rate is at least 3% of pay and increases by 1 percentage point per year until it reaches at least 10%. You can opt out or pick a different rate. Small employers with 10 or fewer employees, businesses less than three years old, and church and governmental plans are exempt.
Employers can also treat your qualified student loan payments as elective deferrals for matching purposes. If you can’t afford to contribute to your retirement plan because of student debt, your employer can still deposit matching contributions based on your loan payments, provided the plan has been amended to include the feature. The match follows the same vesting schedule as other employer contributions.