A 401k is a retirement savings account offered through your employer. You elect to contribute a percentage of each paycheck before taxes are withheld, lowering your taxable income today, and that money grows untaxed until you withdraw it in retirement. For most working Americans, it is the primary retirement savings vehicle available, and the employer match that often comes with it is the closest thing to free money the tax code offers.
The mechanics: how money flows in and out
When you enroll, you choose a contribution percentage, say, 6% of your salary. Each paycheck, that percentage is withheld before federal (and usually state) income tax is calculated. If you earn $5,000 per month and contribute 6%, you put $300 into the account, but your take-home pay drops by only roughly $225, because you no longer owe income tax on that $300.
Inside the account, you choose from a menu of mutual funds, index funds, and target-date funds your employer has selected. The money grows tax-deferred: no capital gains tax, no dividend tax, no annual bill while it stays in the account.
In retirement, withdrawals are taxed as ordinary income. If your income is lower in retirement than during your working years, as it often is, you pay tax at a lower rate than you would have during accumulation.
2026 contribution limits
The IRS adjusts 401k limits annually for inflation. For 2026:
| Contribution type | 2026 limit | 2025 limit |
|---|---|---|
| Employee deferral (under 50) | $24,500 | $23,500 |
| Catch-up contribution (age 50–59, 64+) | +$8,000 | +$7,500 |
| Super catch-up (age 60–63, SECURE 2.0) | +$11,250 | +$11,250 |
| Total employee (age 50+, standard) | $32,500 | $31,000 |
| Total employee (age 60–63) | $35,750 | $34,750 |
| Combined employee + employer (under 50) | $72,000 | $70,000 |
The super catch-up for ages 60–63 was introduced by the SECURE 2.0 Act of 2022. If you’re in that window and your plan supports it, you can contribute $11,250 in catch-up contributions instead of the standard $8,000, a meaningful boost for anyone closing in on retirement with ground to make up.
Most people contribute well below the maximum. Even 6–10% of salary, consistently invested in low-cost index funds, builds substantial wealth over a 30–40 year career.
Employer matching: the most important number in your plan
Most employers match a portion of your contributions. According to Vanguard’s 2024 research, the average employer contribution is 4.6% of salary; Fidelity’s data puts it at 4.7%. Common match structures:
- Dollar-for-dollar up to 3–4%: Contribute 4%, get 4% free
- 50% match up to 6%: Contribute 6%, get 3%, still a 50% instant return
- Tiered matches: 100% on the first 3%, 50% on the next 2%
If you are not contributing enough to capture the full match, you are declining part of your compensation. The Bureau of Labor Statistics reports 41% of plans match up to 6% of salary, if yours is one of them and you’re only contributing 4%, you’re forfeiting 2% of your salary every year.
Fidelity recommends saving 15% of pre-tax income for retirement in total, including the employer match. If your employer contributes 4%, you need to save 11% yourself to reach that target.
Traditional 401k vs. Roth 401k
If your employer offers both options, the choice comes down to when you pay taxes:
| Traditional 401k | Roth 401k | |
|---|---|---|
| Contributions | Pre-tax (reduces income tax now) | After-tax (no immediate tax break) |
| Growth | Tax-deferred | Tax-free |
| Withdrawals in retirement | Taxed as ordinary income | Completely tax-free |
| Required minimum distributions | Yes, starting at age 73 or 75 | No RMDs (as of 2024, SECURE 2.0) |
| Best for | Higher income now, expect lower tax rate in retirement | Lower income now, expect higher tax rate in retirement |
Early in a career, lower income, retirement far away, the Roth typically wins. Tax-free growth over 30 years usually outweighs the smaller immediate tax deduction. Later, when income peaks and the deduction has more value, the traditional 401k often makes more sense. If you’re uncertain, splitting contributions between both hedges against future tax rate changes.
Vesting schedules: not all employer money is immediately yours
Your own contributions are always 100% yours from day one. Employer contributions are different, many plans require you to stay employed for a period before you’re fully entitled to keep the match. According to Vanguard’s 2024 plan data:
- 49% of plans use immediate vesting, the employer match is yours from the first dollar
- 16% use a five-year graded schedule, your percentage of the match vests in increments over five years
- 9% use a three-year cliff, you own nothing of the employer match until year three, then 100% vests at once
The IRS sets maximum vesting periods: cliff vesting cannot exceed three years; graded vesting must complete by six years. Check your summary plan description before leaving a job. If you’re six months from full vesting on a meaningful employer balance, that timeline may be worth factoring into any job change decision.
Early withdrawal: the cost of cashing out early
Withdrawing from a 401k before age 59½ triggers a 10% early withdrawal penalty on top of ordinary income tax. On a $30,000 withdrawal, if you’re in the 22% federal tax bracket, you’d owe $6,600 in income tax plus $3,000 in penalty, $9,600 out of $30,000, before any state taxes.
Common exceptions that reduce or eliminate the penalty include death, permanent disability, substantially equal periodic payments (Rule 72(t)), and qualified domestic relations orders. A first home purchase is not an exception for 401k accounts, that applies to IRAs only.
A 401k loan avoids the 10% penalty but you repay it with after-tax dollars and lose compounding on the borrowed balance. Use it only in genuine emergencies.
Required minimum distributions (RMDs)
The IRS does not allow tax-deferred money to stay sheltered indefinitely. At a certain age, you must begin taking required minimum distributions (RMDs) each year, calculated from your account balance and IRS life expectancy tables.
Under SECURE 2.0:
- If you were born between 1951 and 1959, RMDs begin at age 73
- If you were born in 1960 or later, RMDs begin at age 75
- Missing an RMD carries a 25% excise tax on the amount you failed to take (reduced to 10% if corrected within two years)
- Roth 401k accounts are now exempt from RMDs as of January 2024
RMDs force taxable income in retirement whether you need the cash or not. If you have large traditional balances, a Roth conversion ladder in lower-income years before RMDs begin can reduce the future tax burden.
When you leave a job: four options for your old 401k
| Option | Pros | Cons |
|---|---|---|
| Roll to new employer’s 401k | Simple, one account | New plan’s fund options may be limited |
| Roll to IRA | Wider investment choice, full control | Slightly more admin to set up |
| Leave it where it is | No action required | Multiple accounts to track |
| Cash out | Immediate access | Taxes + 10% penalty wipe out 25–40% immediately |
Cashing out is almost never the right move. A $25,000 balance at age 30, left to grow for 35 years at 9% annually, becomes roughly $494,000 by age 65. Cashing out nets perhaps $16,000 after taxes and penalties.
What to watch out for
Defaulting to the wrong fund. Many plans auto-enroll employees into a money market fund or a conservative bond fund, not a growth-oriented investment. Check what you’re actually invested in. For most people under 55, a target-date fund set to your approximate retirement year, or a simple index fund, is more appropriate than holding primarily cash.
Ignoring the plan after enrollment. Contribution rates and investment choices can be changed at any time. If you got a raise, increase your contribution rate. If you’ve never looked at your investment allocation, look now.
Borrowing from your 401k for non-emergencies. Loans feel low-stakes because you’re “repaying yourself,” but you lose the compounding on the borrowed balance for the entire loan period, and if you leave your job, the loan typically becomes due within 90 days or is treated as a distribution (triggering taxes and penalties).
Underestimating vesting. Job-hopping every two years can mean perpetually forfeiting employer contributions if your plans use cliff or graded vesting. Factor unvested balances into any salary negotiation when switching employers.
Getting started
If you’re new to your employer’s 401k, take these four steps:
- Enroll and contribute at least the full employer match amount, if they match up to 5%, contribute 5%. Do this before anything else.
- Check your investment election. If you were auto-enrolled, confirm you’re not sitting in a money market fund. Select a target-date fund (e.g., “Target 2055 Fund” if you plan to retire around 2055) or a broad US index fund.
- Increase your contribution rate by 1% per year. Most plan providers let you set automatic annual increases. Going from 5% to 6% to 7% over three years is barely noticeable in your paycheck and meaningfully changes your retirement outcome.
- Read your vesting schedule. It takes five minutes and tells you exactly when employer contributions become fully yours, useful information before any career decision.
The 401k is not complicated. The tax deferral, the employer match, and the long compounding runway do most of the work, but only if you contribute enough to activate the match, invest in something that actually grows, and leave it alone until retirement.