An employer-sponsored, tax-advantaged retirement savings plan that allows employees to defer pre-tax (Traditional) or post-tax (Roth) wages into investment accounts, often with an employer match.
A 401(k) plan is the most common employer-sponsored retirement vehicle in the United States. Named after Section 401(k) of the Internal Revenue Code (added by the Revenue Act of 1978 and first widely used in the 1980s), it allows employees to defer a portion of their wages into a tax-advantaged account that grows on a tax-deferred basis. As of 2024, over 70 million American workers participate in 401(k) plans holding more than $7 trillion in retirement assets. For most US employees, the 401(k) is their single largest financial asset by retirement.
Employees elect a percentage of each paycheck (or a flat dollar amount) to defer. The plan offers two flavors of contributions:
• Traditional (pre-tax): Contributions reduce current taxable income — employees see lower federal income tax in their current paycheck. Investment gains compound tax-free until withdrawal. Distributions in retirement are taxed as ordinary income • Roth: Contributions are made with after-tax dollars (no current-year deduction). Investment gains compound tax-free, AND qualified withdrawals in retirement are completely tax-free. The Roth option was added by EGTRRA in 2001 and SECURE 2.0 expanded it significantly
Most plans offer both, and employees can split contributions between them. Choosing depends on current vs expected retirement marginal rates: lower current rates favor Roth, higher current rates favor Traditional.
The IRS sets annual contribution limits indexed for inflation:
• 2024 Elective Deferral Limit: $23,000 ($23,500 for 2025) • Catch-up Contribution (age 50+): additional $7,500 in 2024 ($7,500 in 2025) • Super Catch-up (ages 60-63 under SECURE 2.0): additional $11,250 starting 2025 — replaces the regular catch-up for that age band • Combined employer + employee limit (415(c)): $69,000 in 2024 ($70,000 in 2025), or $76,500 with catch-up • Compensation limit (401(a)(17)): $345,000 in 2024 ($350,000 in 2025) — the maximum compensation that can be considered for plan purposes
Employer matches and contributions vary widely. Common patterns:
• Match: dollar-for-dollar (100%) up to a certain percentage of salary, OR 50¢ per dollar up to a higher cap. A 'classic' match might be 100% of the first 3% plus 50% of the next 2% — 4% total • Non-elective: a flat percentage (often 3%) given to all eligible employees regardless of their own contributions • Profit-sharing: discretionary additional contributions tied to company performance, typically allocated by compensation
Vesting schedules determine when employer contributions become the employee's property:
• Immediate: 100% vested from day one (mandatory for Safe Harbor matches and SIMPLE plans) • Cliff: 100% vested after a specific period, typically 3 years (0% before) • Graded: incremental, e.g., 20% after 2 years, 40% after 3, 60% after 4, 80% after 5, 100% after 6 — the maximum allowable graded schedule under ERISA
Employee deferrals are always 100% vested immediately — that's the employee's own money.
401(k) plans are subject to ERISA (Employee Retirement Income Security Act of 1974), which imposes fiduciary duties, reporting, and disclosure requirements. The plan sponsor is a fiduciary and must act prudently and solely in participants' interest. Common ERISA obligations:
• Annual Form 5500 filing with the DOL — discloses plan financials, participant counts, investments • Summary Plan Description (SPD) given to all participants — explains the plan in plain language • Summary Annual Report (SAR) — abbreviated annual summary • Investment policy statement and prudent investment selection (often delegated to an investment advisor under §3(38) or §3(21)) • Non-discrimination testing — ADP (Actual Deferral Percentage) and ACP (Actual Contribution Percentage) tests ensure highly compensated employees don't disproportionately benefit • Top-heavy testing — if 60%+ of plan assets belong to 'key employees' (officers and 5%+ owners), additional minimum contributions are required
Non-discrimination testing is the biggest pain point for small and mid-sized employers. If HCEs (Highly Compensated Employees, defined as anyone earning over $155,000 in 2024 or owning 5%+ of the company) defer too much relative to NHCEs (everyone else), the plan must either return excess deferrals to HCEs (with associated tax consequences) or make corrective contributions to NHCEs. Both are unwanted.
Safe Harbor 401(k) plans avoid most non-discrimination testing by adopting one of three pre-approved structures:
• Safe Harbor Match: 100% of first 3% + 50% of next 2% (4% total), OR 100% of first 4% (4% total), OR a more generous formula. All Safe Harbor matches must be 100% immediately vested • Safe Harbor Non-Elective: 3% non-elective contribution to all eligible employees regardless of their own deferrals • QACA Safe Harbor: more flexible vesting (cliff up to 2 years allowed)
Safe Harbor plans dominate the small-business 401(k) market because they eliminate the testing risk. Setup typically requires a notice to employees 30-90 days before the plan year begins.
Loans from 401(k) accounts are permitted (at the plan's discretion) up to the lesser of $50,000 or 50% of the vested account balance. Loans must be repaid with interest within 5 years (longer for primary residence purchase). Default on a loan converts the unpaid balance to a taxable distribution plus 10% early-withdrawal penalty if under age 59½.
Early withdrawals (before age 59½) are subject to ordinary income tax plus a 10% early-withdrawal penalty, with limited exceptions (death, disability, medical expenses over 7.5% AGI, qualified domestic relations orders, certain birth/adoption, certain natural disasters under SECURE 2.0). Required Minimum Distributions begin at age 73 (75 for those born 1960 or later, under SECURE 2.0).
The SECURE Act (2019) and SECURE 2.0 (2022) made significant changes: automatic enrollment is now required for new plans starting 2025; long-term part-time employees must be allowed to defer; small employer tax credits expanded; emergency savings accounts within 401(k) plans authorized; student loan payments can trigger employer matching contributions.
Common 401(k) providers serving the SMB market: Guideline, Human Interest, Vestwell, Fidelity, Schwab Workplace, ADP Retirement Services, Empower, Principal. Modern HR platforms integrate with these providers via SFTP or API to sync deferrals each pay period — auto-enrolling new hires per the plan's eligibility rules, processing changes in deferral elections, applying the right vesting schedule on terminations.
Our 401(k) plan offers a 4% Safe Harbor match (100% of the first 3% plus 50% of the next 2%) fully vested immediately, integrated with Guideline and synced to payroll each cycle. We auto-enroll new hires at 6% deferral with auto-escalation of 1% per year up to 10%.
Peoplifi unifies HR, payroll, time tracking, and performance into one modern platform — so concepts like 401(k) stay handled, not stuck in spreadsheets.
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