What Is a 401k and How Does It Work?

A 401k is an employer-sponsored retirement savings account that allows employees to contribute a portion of their paycheck before taxes are taken out. It is named after the section of the Internal Revenue Code that created it and it has become the primary retirement savings vehicle for most American workers. Understanding how a 401k works — and more importantly how to use it effectively — is one of the most financially valuable things any working person can do.

How 401k Contributions Work

When you contribute to a traditional 401k the money is deducted from your paycheck before federal and state income taxes are calculated. If you earn $3,000 per paycheck and contribute $300 to your 401k you only pay income tax on $2,700. The $300 goes into your retirement account and grows tax-deferred — meaning you pay no taxes on the growth until you withdraw the money in retirement. This pre-tax contribution reduces your current taxable income while building retirement savings simultaneously.

The annual contribution limit for 2026 is $23,500 for employees under 50 with an additional catch-up contribution of $7,500 allowed for employees 50 and older. Most people do not contribute the maximum — the median 401k contribution rate is around 6 to 8 percent of salary — but even modest consistent contributions compound significantly over a 30 to 40 year career.

The Employer Match — Free Money You Cannot Afford to Leave

Many employers offer a matching contribution to employee 401k accounts — the most common structure is matching 50 cents for every dollar the employee contributes up to 6 percent of salary. On a $50,000 salary contributing 6 percent means contributing $3,000 per year and receiving a $1,500 employer match — a 50 percent immediate return on your contribution before any market growth occurs. This is the single highest guaranteed return available to most working people and failing to contribute at least enough to capture the full match is leaving significant compensation on the table.

Traditional vs Roth 401k

Many employers now offer both traditional and Roth 401k options. Traditional contributions are pre-tax and reduce current taxable income — taxes are paid when money is withdrawn in retirement. Roth contributions are made with after-tax money and do not reduce current taxable income — but the money grows tax-free and qualified withdrawals in retirement are completely tax-free. Which is better depends primarily on whether you expect to be in a higher or lower tax bracket in retirement than you are today. Most financial advisors suggest Roth contributions are more beneficial earlier in a career when income and tax rates are lower.

Vesting Schedules — When the Match Is Actually Yours

Employer matching contributions often come with a vesting schedule — a timeline before the matched funds become fully yours. Immediate vesting means the match is yours from day one. Cliff vesting means none of the match is yours until you have worked for the employer for a specific period — often two to three years — after which it becomes 100 percent yours. Graded vesting means the match becomes yours incrementally over a multi-year schedule. Understanding your employer's vesting schedule matters if you are considering leaving a job — unvested employer contributions are forfeited when you leave.

What Happens to Your 401k When You Change Jobs

When you leave an employer you have several options for your 401k balance. You can leave it with your former employer if the plan allows and the balance meets minimum thresholds. You can roll it over to your new employer's 401k plan. You can roll it over to an individual IRA which typically offers more investment options. You can cash it out — which triggers income taxes plus a 10 percent early withdrawal penalty if you are under 59.5 years old and is almost never the right choice.