What is a 401(k)
A 401(k) is an employer-sponsored retirement savings plan that allows workers to invest a portion of their paycheck before taxes are taken out, with contributions growing tax-deferred until withdrawal in retirement.
A 401(k) is an employer-sponsored, tax-advantaged retirement savings account that allows workers to set aside a portion of their paycheck to invest for retirement. Contributions are made pre-tax (reducing your taxable income today), and the money grows tax-deferred — meaning you don't pay taxes on investment gains until you make withdrawals in retirement. It is one of the most powerful wealth-building tools available to American workers.
The name comes from the section of the Internal Revenue Code that established the plan type: Section 401(k).
How a 401(k) Works
- You elect to contribute a percentage of your paycheck (e.g., 6%)
- Your employer deducts that amount before calculating income taxes
- The money goes into your 401(k) account, where you choose how to invest it from a menu of options (typically mutual funds and index funds)
- The investments grow tax-deferred for decades
- In retirement (typically starting at age 59½), you withdraw funds and pay ordinary income tax on the distributions
Contribution Limits (2025)
The IRS sets annual contribution limits:
- Under age 50: $23,500 per year
- Age 50 and older: $31,000 per year (includes a $7,500 catch-up contribution)
These limits apply only to employee contributions — employer matches are additional.
Employer Match: Free Money
Many employers offer a 401(k) match — they contribute a percentage matching your own contributions up to a certain limit. For example, an employer might match 100% of contributions up to 3% of your salary. If you earn $60,000 and contribute 3% ($1,800), your employer adds another $1,800 — for a total of $3,600 invested annually before you've seen a dollar of actual investment return.
Not contributing at least enough to capture the full employer match is widely considered one of the most common personal finance mistakes — it's leaving compensation on the table.
Traditional 401(k) vs. Roth 401(k)
Many employers now offer both options:
| Feature | Traditional 401(k) | Roth 401(k) |
|---|---|---|
| Contributions | Pre-tax | After-tax |
| Growth | Tax-deferred | Tax-free |
| Withdrawals | Taxed as income | Tax-free (if qualified) |
| Best for | Those in a higher tax bracket now | Those expecting higher taxes in retirement |
The Roth IRA follows similar logic to the Roth 401(k) — contributions are after-tax but growth and qualified withdrawals are tax-free.
Investment Options
401(k) plans offer a menu of investment choices selected by the plan administrator. Most workers invest primarily in:
- Target-date funds — automatically shift from growth to conservative as you approach retirement
- Index funds — broad market exposure at low cost (see index fund)
- Mutual funds — actively managed portfolios
Low-cost index funds are generally recommended for most 401(k) investors due to their low expense ratios and reliable long-term performance.
Early Withdrawal Penalties
Withdrawing from a 401(k) before age 59½ typically triggers:
- A 10% early withdrawal penalty
- Ordinary income taxes on the amount withdrawn
There are some exceptions (hardship withdrawals, certain life events), but in general, 401(k) funds should be treated as untouchable until retirement.
Rolling Over a 401(k)
When you leave an employer, you can roll over your 401(k) into a new employer's plan or into an individual retirement account (IRA) without triggering taxes. This is typically the best option, as it preserves the tax-advantaged status of the money. Fidelity and Vanguard are among the most popular destinations for 401(k) rollovers due to their low-cost fund offerings. If you roll into a Traditional IRA, you may later consider a Roth IRA conversion to move pre-tax funds into Roth status — a strategy worth evaluating in lower-income years.
The Power of Compounding Inside a 401(k)
Because a 401(k) grows tax-deferred, compound interest works more efficiently inside it than in a taxable brokerage account — taxes don't drag on the growth annually. Over a 30–40 year career, this tax-deferred compounding can result in significantly larger balances than equivalent investments held in a taxable account.