Yes, most 401(k) contributions are deducted before taxes

When you contribute to a traditional 401(k), the money comes out of your paycheck before your employer calculates federal income tax, Social Security tax, and Medicare tax. That means your taxable income for the year is lower by the amount you contributed. If you earn $60,000 and put $7,000 into a traditional 401(k), you only report $53,000 as taxable income to the IRS.

This is different from putting money into a savings account or a regular investment account, where you pay taxes on your income first and then save what's left. With a traditional 401(k), you get the tax break upfront — but you will owe taxes on the money when you withdraw it in retirement.

A Roth 401(k) works the opposite way: contributions come out of your paycheck after taxes are already taken out, so they do not lower your taxable income now. The tradeoff is that withdrawals in retirement are tax-free. Some employers offer both types, and you can split your contributions between them.

Key Takeaways

  • Traditional 401(k) contributions reduce your taxable income in the year you make them, lowering the federal income tax you owe that year.
  • Roth 401(k) contributions do not reduce your taxable income now, but withdrawals in retirement are tax-free.
  • Your employer withholds taxes based on your reduced income if you use a traditional 401(k), so your take-home paycheck is larger than it would be if you saved the same amount outside a retirement plan.
  • The IRS sets annual limits on how much you can contribute to a 401(k); for 2024 the limit is $23,500 for people under 50 and $31,000 for people 50 and older.
  • When you withdraw money from a traditional 401(k) in retirement, that withdrawal counts as income and is taxed at your ordinary income tax rate.

How the pre-tax deduction affects your paycheck

Because your 401(k) contribution lowers your taxable income, your employer withholds less federal income tax from your paycheck. If you normally have $200 withheld per paycheck and you start contributing $300 per paycheck to a traditional 401(k), your federal withholding will drop — you might see only $150 withheld instead. Your take-home pay does not drop by the full $300 because you are paying less in taxes.

This is one reason a traditional 401(k) can feel less painful than saving the same amount in a regular bank account. You are not paying taxes on the money you set aside, so the actual reduction in your paycheck is smaller than the contribution itself.

Social Security and Medicare taxes (collectively called payroll taxes) are not reduced by 401(k) contributions — those are calculated on your full gross income. Only federal income tax, and in some cases state income tax, gets reduced.

The difference between traditional and Roth 401(k)s

A traditional 401(k) gives you a tax break now. You contribute pre-tax dollars, your taxable income drops, and you pay less in taxes this year. When you retire and start withdrawing the money, each withdrawal is taxed as ordinary income.

A Roth 401(k) gives you a tax break later. You contribute after-tax dollars — your paycheck is reduced by the full amount, and your taxable income does not change. But when you withdraw money in retirement, you owe no federal income tax on it, including the growth it earned over the years.

Which one makes sense depends on whether you expect to be in a higher or lower tax bracket in retirement. If you think you will earn less in retirement than you do now, a traditional 401(k) might save you more total tax. If you think you will earn the same or more, or if tax rates rise, a Roth might be better. Many people split contributions between both types to hedge their bet.

Contribution limits and how they work

The IRS sets an annual limit on how much you can contribute to a 401(k). For 2024, the limit is $23,500 if you are under 50 years old, and $31,000 if you are 50 or older (the extra $7,500 is called a catch-up contribution). These limits explore to the total of all your 401(k) accounts combined — if you have two jobs with two 401(k) plans, your contributions to both plans together cannot exceed the limit.

The limit applies only to employee contributions. If your employer matches part of your contribution, that match does not count toward your limit. Your employer can contribute up to an additional $69,000 per year (as of 2024), though most employers contribute far less.

If you exceed the limit, the excess contributions are taxed twice — once when you contribute and again when you withdraw — so it is important to track your total across all plans if you have more than one.

When you will pay taxes on 401(k) money

With a traditional 401(k), you postpone taxes, not avoid them. When you withdraw money in retirement, the IRS treats that withdrawal as income for that year. If you withdraw $50,000 from your 401(k) in a given year, that $50,000 is added to any other income you have (Social Security, pensions, part-time work) and taxed at your ordinary income tax rate.

The IRS requires you to start taking withdrawals at age 73 (as of 2023; this age has been rising gradually). These are called required minimum distributions, or RMDs. The amount you must withdraw each year is calculated based on your age and account balance, and you cannot avoid it without paying a penalty.

If you have a Roth 401(k), you do not owe federal income tax on withdrawals in retirement. You also do not have to take required minimum distributions during your lifetime, which gives you more control over when and how much to withdraw.

State income tax and 401(k) contributions

Most states that have an income tax also allow 401(k) contributions to reduce your state taxable income, just as they reduce your federal income. A few states — including Illinois, Pennsylvania, and New Hampshire — do not tax retirement income at all, which changes the math for people who live there.

If you work in one state but live in another, the rules can get complicated. Generally, the state where you work withholds taxes based on where you work, but you file a return in the state where you live. A tax professional can help you sort this out if you are in that situation.

What happens if you withdraw money early

If you withdraw money from a traditional 401(k) before age 59½, you owe federal income tax on the withdrawal plus a 10 percent early withdrawal penalty. A $10,000 early withdrawal might cost you $2,000 to $3,000 in taxes and penalties, depending on your tax bracket.

There are a few exceptions: you can withdraw without penalty if you are disabled, if you are withdrawing to cover certain medical expenses, or if you are taking substantially equal periodic payments. Some plans also allow loans, where you borrow from your own 401(k) and pay yourself back with interest.

Roth 401(k)s have the same early withdrawal penalty on earnings, but you can withdraw your contributions (the money you put in) at any time without penalty, since you already paid taxes on it.

How to understand your 401(k) statement

Your 401(k) statement shows your contributions, your employer's match, investment gains or losses, and your current balance. The contributions line tells you how much you have set aside pre-tax (or after-tax if you have a Roth). Your paycheck stub shows the 401(k) deduction separately from your federal income tax withholding, so you can see both numbers.

If you are unsure whether your contributions are being handled correctly, compare your paycheck stub to your 401(k) statement. The contribution amount should match. If your employer offers both traditional and Roth options and you chose to split between them, your statement should show both balances separately.

Frequently Asked Questions

Can I deduct 401(k) contributions on my tax return?

No. Traditional 401(k) contributions are deducted automatically by your employer before you file your tax return. Your W-2 form shows your income after the 401(k) deduction has already been taken out. You do not claim the deduction yourself on your return.

Does a 401(k) reduce my Social Security taxes?

No. Social Security and Medicare taxes (payroll taxes) are calculated on your full gross income, regardless of 401(k) contributions. Only federal and state income taxes are reduced by traditional 401(k) contributions.

What if I contribute to both a 401(k) and an IRA?

You can contribute to both. The annual limits are separate — the 401(k) limit and the IRA limit do not affect each other. However, if you have a traditional IRA and a 401(k), your ability to deduct IRA contributions may be limited depending on your income. A tax professional can help you understand the rules for your situation.

If I switch jobs, what happens to my 401(k) tax deduction?

Your previous employer's 401(k) stays as it is — the tax deduction already happened when you contributed. Your new employer's 401(k) is a separate plan with separate contribution limits. You can roll your old 401(k) into your new employer's plan or into an IRA, and the rollover itself is not taxed.

Does a Roth 401(k) ever give me a tax deduction?

No. Roth 401(k) contributions are made with after-tax dollars, so they do not reduce your taxable income. The benefit comes later, when you withdraw the money in retirement tax-free.