How 401(k) Contributions Lower Your Taxable Income

Yes, most 401(k) contributions reduce the income you report to the IRS

When you contribute to a traditional 401(k), the money comes out of your paycheck before federal income tax is calculated. That means your employer reports a lower taxable income to the IRS, and you pay less in federal income tax that year. The contribution itself is not taxed until you withdraw the money in retirement.

A Roth 401(k) works differently. You contribute after-tax dollars, so the contribution does not lower your taxable income now. But the money grows tax-free, and you withdraw it tax-free in retirement. The choice between traditional and Roth depends on whether you expect to be in a higher or lower tax bracket when you retire.

Your employer may also match part of your contribution. Employer matching is always made to a traditional 401(k) on a pre-tax basis, regardless of whether you chose traditional or Roth contributions for your own money.

Key Takeaways

• Traditional 401(k) contributions reduce your taxable income in the year you make them, lowering your federal income tax bill.
• Roth 401(k) contributions do not lower your current taxable income, but the withdrawals in retirement are tax-free.
• Your employer's matching contribution is always pre-tax and reduces your taxable income, even if you chose Roth for your own contributions.
• The IRS sets annual contribution limits, which vary by year and are higher for people age 50 and older.

How the tax deduction works on your paycheck

Your payroll department withholds your traditional 401(k) contribution before calculating federal income tax withholding. If you earn $3,000 in a pay period and contribute $300 to a traditional 401(k), your employer calculates federal income tax on $2,700, not $3,000. This is called a "pre-tax" contribution.

The contribution still appears on your W-2 form at the end of the year, but in a separate box that reduces your taxable wages. When you file your tax return, your taxable income is already lower because of these contributions. You do not need to claim a deduction on your tax return—the reduction happens automatically through payroll.

State and local income taxes work the same way in most states. However, a few states do not tax retirement income, so the rules vary. Check your state's tax agency website if you live in a state with income tax and want to know the exact treatment.

Roth contributions and current taxes

When you choose a Roth 401(k), your contribution is withheld after federal income tax is calculated. If you earn $3,000 and contribute $300 to a Roth 401(k), your employer calculates federal income tax on the full $3,000. You pay more in taxes now, but you owe nothing on the money when you withdraw it later.

Roth contributions make sense if you believe you will be in a higher tax bracket in retirement, or if you want to reduce the size of your taxable estate. They also give you more flexibility in retirement because you can withdraw your contributions (not the earnings) without penalty at any age, though earnings are subject to the normal Roth withdrawal rules.

Some employers offer both traditional and Roth 401(k)s. You can split your contributions between the two, as long as your total does not exceed the annual limit set by the IRS.

Contribution limits and who can deduct

The IRS sets a maximum amount you can contribute to a 401(k) each year. For 2024, that limit is $23,500 for people under age 50. People age 50 and older can contribute an additional $7,500 as a "catch-up" contribution, for a total of $31,000. These limits change periodically, so check the IRS website or your plan documents if you are planning for a future year.

Your employer may also set a lower limit, or may not allow Roth contributions at all. Check your plan's summary plan description, which your HR or benefits department can provide, to see what options your specific plan offers.

If you are self-employed or own a small business, you may have a Solo 401(k) or SEP-IRA instead. The deduction rules are similar, but the contribution limits and calculations are different. Consult a tax professional or your plan administrator if you are self-employed.

What happens when you withdraw the money

Traditional 401(k) withdrawals are taxed as ordinary income. If you withdraw $10,000 from a traditional 401(k), that $10,000 is added to your taxable income for the year, and you pay federal income tax on it at your current tax rate. You also owe state income tax in most states.

You must start taking withdrawals from a traditional 401(k) by April 1 of the year after you turn 73. These are called required minimum distributions (RMDs), and the IRS calculates the amount based on your age and account balance. If you do not take the full RMD, you owe a penalty on the amount you should have withdrawn.

Roth 401(k) withdrawals of earnings are tax-free if you have held the account for at least five years and are age 59½ or older. You can withdraw your contributions at any time without tax or penalty. Like traditional 401(k)s, Roth 401(k)s require RMDs starting at age 73, though you can roll the Roth 401(k) into a Roth IRA to avoid RMDs.

How employer matching affects your taxes

Your employer's matching contribution is always made on a pre-tax basis. Even if you chose a Roth 401(k) for your own contributions, your employer's match goes into a traditional 401(k) portion of your account and reduces your taxable income. This is one reason some people contribute to both traditional and Roth within the same plan.

Employer matching is not counted toward your personal contribution limit. If you contribute $10,000 and your employer matches $5,000, only your $10,000 counts against the annual limit. The $5,000 match is separate and does not reduce the amount you can contribute.

Some employers use a vesting schedule, which means you do not own the matching contribution immediately. You may need to work for the company for a certain number of years before the match is fully yours. Check your plan documents to see your vesting schedule.

Frequently Asked Questions

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

No. Traditional 401(k) contributions are deducted automatically through payroll before your taxes are calculated. You do not claim them as a deduction on your tax return. The reduction is already reflected in your W-2 form and your taxable income.

Do I pay Social Security and Medicare taxes on 401(k) contributions?

Yes. Traditional 401(k) contributions reduce your federal income tax, but you still pay Social Security tax (6.2% up to a wage cap) and Medicare tax (1.45%) on the full amount of your paycheck, including the contribution amount.

What if I have both a traditional and Roth 401(k) at the same employer?

Your combined contributions to both accounts cannot exceed the annual limit. If you contribute $12,000 to traditional and $11,500 to Roth, your total is $23,500 (the 2024 limit), and you cannot contribute more that year. The employer match is separate and does not count toward this limit.

Does a 401(k) contribution reduce my taxable income for state taxes?

In most states, yes. Traditional 401(k) contributions reduce both federal and state taxable income. However, a few states do not tax retirement income or treat 401(k)s differently. Check your state's tax agency website or ask your HR department about your specific state's rules.

Can I deduct 401(k) contributions if I also have an IRA?

401(k) contributions are deducted automatically and do not affect IRA deduction rules. However, if you have a traditional IRA and are covered by a 401(k) at work, your IRA contribution deduction may be limited based on your income. This is called the "phase-out" rule. Roth IRA contributions are not deductible regardless of 401(k) coverage.