The 401(k) plan started with the Revenue Act of 1978, which added Section 401(k) to the Internal Revenue Code. The provision did not take effect until January 1, 1980, and the first working 401(k) plan was designed in 1981 by benefits consultant Ted Benna after the IRS issued regulations explaining how employers could actually run one.1Office of the Law Revision Counsel. 26 USC 401 – Qualified Pension, Profit-Sharing, and Stock Bonus Plans
The 1978 Statute That Created Section 401(k)
Congress passed the Revenue Act of 1978 as Public Law 95-600, and buried inside it was a new subsection of the tax code: Section 401(k). The language defined a “qualified cash or deferred arrangement” that could sit inside a profit-sharing or stock bonus plan. An employee covered by such an arrangement could elect to have the employer contribute a portion of pay into a trust instead of receiving that money as cash wages. Contributions made through the employee’s election had to be nonforfeitable, meaning the deferred money belonged to the worker and could not be clawed back by the employer.1Office of the Law Revision Counsel. 26 USC 401 – Qualified Pension, Profit-Sharing, and Stock Bonus Plans
Although the law was signed in 1978, Section 401(k) had a delayed effective date. It became operative on January 1, 1980. So the earliest possible date any 401(k)-style arrangement could legally exist under the new tax code section is 1980.
Why Congress Added the Provision
Section 401(k) was written to fix a specific technical problem. Some companies already offered cash-option profit-sharing plans, where an employee could take a bonus in cash or defer it into a profit-sharing trust. The IRS had treated these arrangements inconsistently, and the tax result depended on how the agency characterized each plan. Section 401(k) resolved that inconsistency by laying down uniform rules for when a deferral election would keep the money out of the employee’s current taxable income.
Legislative records suggest lawmakers saw this as a narrow cleanup for corporate profit-sharing, not the start of a new retirement system. Few in Congress anticipated that the provision would grow into the primary retirement vehicle for tens of millions of private-sector workers.
1981: The IRS Rules and the First Real 401(k) Plan
The statute took effect in 1980, but employers had no operational guidance for setting up a plan. That gap closed on November 10, 1981, when the IRS issued proposed regulations describing how workers could contribute a portion of their wages on a pre-tax basis through payroll deductions. The regulations confirmed that income diverted into these accounts would not count as gross income for federal tax purposes until the employee later withdrew it, and they framed the arrangement as a Cash or Deferred Arrangement.2Internal Revenue Service. Treasury Decision 9169 – Cash or Deferred Arrangements
Ted Benna, a benefits consultant, used the 1978 statute together with the 1981 IRS guidance to build the first functional 401(k) plan for his own employer, The Johnson Companies. Benna added something the statute itself did not require: an employer matching contribution. The company would put in additional money alongside whatever the employee chose to defer. That match, paired with payroll-deducted pre-tax contributions from regular paychecks, gave workers at every income level a concrete reason to participate. Other corporations copied the design quickly, and the modern 401(k) was in circulation by the early 1980s.
What Existed Before the 401(k)
To understand why 1978 mattered, it helps to know what workplace retirement looked like before then. Most American workers who had employer-provided retirement benefits were covered by traditional defined-benefit pensions. Under a pension, the employer promised a specific monthly payment in retirement based on the worker’s salary and years of service, and the employer bore all of the investment risk. If the plan’s investments underperformed, the company still owed the promised benefit.
Congress had passed the Employee Retirement Income Security Act of 1974 (ERISA) four years before the Revenue Act of 1978. ERISA set federal standards for private pension plans, including rules on reporting, vesting, funding, and fiduciary conduct, aimed at protecting workers from mismanaged or underfunded pensions.3U.S. Department of Labor. History of EBSA and ERISA Even with those safeguards, pensions imposed open-ended long-term obligations on employers. The 401(k) turned out to be a different arrangement entirely: the employee elected how much to defer, chose the investments, and carried the investment risk, while the employer’s cost was limited to the matching contribution it chose to offer.
The shift was substantial. In 1980, roughly 38 percent of private-sector wage and salary workers participated in a defined-benefit pension plan, and only 8 percent were in a defined-contribution plan alone. By 2008, those figures had essentially flipped: pension participation had fallen to 20 percent while defined-contribution-only coverage had risen to 31 percent.4Social Security Administration. The Disappearing Defined Benefit Pension and Its Potential Impact on the Retirement Incomes of Baby Boomers
How the Rules Have Changed Since 1980
The 401(k) that exists today is not the 1978 provision unchanged. Congress has revisited the rules many times, and each round of legislation reshaped how the plans operate.
The Tax Reform Act of 1986
The Tax Reform Act of 1986 (Public Law 99-514) made three lasting changes. It introduced nondiscrimination testing, which stops a plan from disproportionately benefiting highly compensated employees; if top earners defer at much higher rates than everyone else, the employer must correct the imbalance by refunding excess deferrals or by making additional contributions for lower-paid workers. The law also cut the annual elective deferral cap sharply, from $30,000 down to $7,000, to curb excessive tax sheltering. And it added the 10 percent additional tax on early withdrawals under Section 72(t) of the Internal Revenue Code, which applies when a participant takes money out before age 59½, subject to several exceptions including death, disability, an IRS levy, substantially equal periodic payments, high unreimbursed medical expenses, and separation from service at or after age 55.5Office of the Law Revision Counsel. 26 US Code 72 – Annuities; Certain Proceeds of Endowment and Life Insurance Contracts6Internal Revenue Service. Retirement Topics – Exceptions to Tax on Early Distributions
The Roth 401(k) in 2001
The Economic Growth and Tax Relief Reconciliation Act of 2001 (EGTRRA) created the Roth 401(k), though employers could not begin offering one until tax years starting after December 31, 2005.7Internal Revenue Service. EGTRRA and Recent Law Provisions Roth contributions go in on an after-tax basis rather than reducing current taxable income; in exchange, qualified distributions, including investment growth, come out tax-free. To qualify, the account must be held at least five tax years after the first contribution, and the participant must be at least 59½, disabled, or deceased with the distribution paid to a beneficiary.8Internal Revenue Service. Retirement Plans FAQs on Designated Roth Accounts
Automatic Enrollment in 2006
The Pension Protection Act of 2006 tackled a persistent problem: many eligible workers never signed up. The law created a safe harbor allowing employers to enroll workers by default at a set contribution rate unless the worker opted out, and plans using the safe harbor were exempt from nondiscrimination testing. The default rate started at a minimum of 3 percent in the first year and rose by one percentage point per year up to at least 6 percent. Employers using the safe harbor had to either match 100 percent of the first 1 percent of pay and 50 percent of the next 5 percent, or make a flat 3 percent nonelective contribution for every eligible employee, with matching contributions vesting fully within two years. The 2006 Act also authorized qualified default investment alternatives, so auto-enrolled contributions could go into age-appropriate options like target-date funds instead of parking in low-return money market accounts. The provisions applied to plan years beginning after December 31, 2007.
The SECURE Act of 2019
The Setting Every Community Up for Retirement Enhancement (SECURE) Act of 2019 raised the age for required minimum distributions from 70½ to 72 and expanded 401(k) access to long-term part-time workers, requiring plans to allow participation by employees who worked at least 500 hours per year for three consecutive years.
The SECURE 2.0 Act of 2022
SECURE 2.0, enacted in December 2022, went further. For plan years beginning after December 31, 2024, most new 401(k) plans must automatically enroll eligible workers at a default contribution rate between 3 and 10 percent of pay, rising one percentage point each year until it reaches at least 10 percent (and no more than 15 percent).9Federal Register. Automatic Enrollment Requirements Under Section 414A Businesses less than three years old and employers with 10 or fewer employees are exempt from the mandate.10Office of the Law Revision Counsel. 26 US Code 414A – Requirements Related to Automatic Enrollment The law also lifted the required minimum distribution age to 73 for people reaching that age starting in 2023, with a further increase to 75 scheduled for individuals born in 1960 or later.11Internal Revenue Service. Retirement Plan and IRA Required Minimum Distributions FAQs A higher catch-up contribution limit applies to workers aged 60 through 63, and employers may now make matching contributions based on an employee’s qualified student loan payments rather than requiring an actual 401(k) deferral.12Internal Revenue Service. Guidance Under Section 110 of the SECURE 2.0 Act With Respect to Matching Contributions Made on Account of Qualified Student Loan Payments
The through-line from 1978 to today is a plan that Congress originally treated as a minor technical fix and that private employers and later lawmakers turned, decade by decade, into the country’s dominant retirement savings vehicle.