Yes, you must report 401(k) contributions and withdrawals on your taxes, but the reporting method depends on whether the money went in before or after taxes

If you contribute to a traditional 401(k), your employer reports those contributions to the IRS on Form 5498, and you report them on your tax return using Schedule 1 (Form 1040). The contributions reduce your taxable income for that year. When you withdraw money in retirement, those withdrawals count as ordinary income and you owe taxes on them then.

If you contribute to a Roth 401(k), you do not get a tax deduction for the contributions now, but withdrawals in retirement are tax-free. You still report the contributions to show the IRS you made them, but they do not lower your taxable income this year.

Your employer sends you a statement each year showing how much you contributed and how much you withdrew. The IRS gets a copy too. If the numbers do not match what you report, the IRS will notice.

Key Takeaways

  • Traditional 401(k) contributions reduce your taxable income this year, but withdrawals are taxed as income when you take them out.
  • Roth 401(k) contributions do not lower your taxes now, but may have access to withdrawals in retirement are completely tax-free.
  • Your employer reports your 401(k) activity to the IRS on Form 5498, so you must report it on your return or face a mismatch notice.
  • If you withdraw money before age 59½ from a traditional 401(k), you owe income tax plus a 10 percent penalty on the amount withdrawn, unless an exception applies.
  • Employer matching contributions are also reported and taxed the same way as your own contributions.

How traditional 401(k) reporting works on your tax return

When you contribute to a traditional 401(k), your employer deducts the money from your paycheck before calculating federal income tax. That means your W-2 form shows a lower gross income than you actually earned. The contributions appear in Box 12 of your W-2 with code D, E, or F depending on the type of deferral.

You do not have to do anything special to claim the deduction — your employer has already done it. However, you should verify that the amount on your W-2 matches what you contributed. If you made contributions to multiple employers in the same year, add them all together. The IRS limit for 2024 is $23,500 (or $31,000 if you are 50 or older), and if you go over, you owe taxes on the excess.

When you withdraw money from a traditional 401(k) after retirement, that withdrawal is reported on Form 1099-R, and you report it as ordinary income on your tax return. You pay income tax on the full amount withdrawn, at whatever your tax rate is that year.

Roth 401(k) contributions and tax reporting

Roth 401(k) contributions come out of your paycheck after taxes have already been withheld. Your employer still reports them on your W-2, but in a different box — usually Box 12 with code AA. Because you already paid taxes on the money, you do not get a deduction.

The advantage shows up later: when you withdraw money from a Roth 401(k) after age 59½ and the account has been open for at least five years, the withdrawal is not taxed. You still receive a Form 1099-R, but the taxable portion is zero. If you withdraw before those conditions are met, you owe taxes and penalties on the earnings portion of the withdrawal, though not on your contributions themselves.

Many people have both a traditional and a Roth 401(k) at the same employer. Report each one separately on your tax return, and keep track of which contributions went into which account.

Early withdrawals and the 10 percent penalty

If you withdraw money from a traditional 401(k) before age 59½, the IRS taxes the withdrawal as ordinary income and adds a 10 percent penalty on top. That penalty is reported on Form 5329 and included in your total tax bill. A $10,000 early withdrawal could cost you $2,000 to $4,000 in taxes and penalties, depending on your tax bracket.

Some situations are exempt from the penalty: disability, death, a series of substantially equal periodic payments (called a SEPP), medical expenses over 7.5 percent of your adjusted gross income, and a few others. If an exception applies, you still owe income tax on the withdrawal, but not the 10 percent penalty. You report the exception on Form 5329 to tell the IRS why you are not paying the penalty.

Roth 401(k) early withdrawals are more complicated. You can withdraw your contributions without penalty at any time, but withdrawals of earnings before age 59½ trigger both income tax and the 10 percent penalty unless an exception applies.

Employer matching contributions and your taxes

When your employer matches your 401(k) contributions, that matching money is also reported on your W-2 and reduces your taxable income for the year, just like your own contributions do. You do not have to do anything — your employer includes it automatically.

The matching contributions count toward the annual contribution limit only if your plan allows it. Most plans do not count employer matching toward the employee limit, so you can contribute $23,500 of your own money plus receive unlimited employer matching (up to the overall plan limit of $69,000 in 2024). Check your plan documents or ask your HR department to confirm how your plan handles this.

What happens if you do not report your 401(k)

The IRS receives a copy of Form 5498 from your employer showing your contributions and a copy of Form 1099-R showing your withdrawals. If you do not report these amounts on your tax return, the IRS will send you a notice saying your return does not match the information they received from your employer.

You will owe the taxes you should have paid, plus interest calculated from the original due date. If the IRS determines the underreporting was intentional, you may also owe a penalty of 20 percent of the underpaid tax. Even if it was a mistake, the interest adds up quickly — currently around 8 percent per year.

The easiest way to avoid this is to check your W-2 and any 1099-R forms you receive against what you contributed and withdrew, and report those amounts on your return. If you received a notice, you can respond by filing an amended return or explaining the discrepancy to the IRS.

Loans from your 401(k) and tax reporting

If you borrow money from your 401(k) rather than withdrawing it, the loan itself is not taxed. However, if you do not repay the loan according to the plan rules, the unpaid balance is treated as a withdrawal and becomes taxable. Your employer reports the loan status on Form 5498.

If you leave your job and have an outstanding 401(k) loan, you typically have 60 days to repay it or it becomes a taxable distribution. That distribution is reported on Form 1099-R, and you owe income tax plus the 10 percent early withdrawal penalty if you are under 59½. Plan ahead if you are considering a loan and may change jobs.

Frequently Asked Questions

Do I report my 401(k) on Schedule C or Schedule 1?

You report 401(k) contributions on Schedule 1 (Form 1040) as an adjustment to income. You do not report it on Schedule C, which is for self-employment income. Your employer has already deducted traditional contributions from your W-2, so the deduction flows through automatically in most cases.

What if I had a 401(k) at two different jobs in the same year?

Add the contributions from both jobs together. If the total exceeds the annual limit ($23,500 in 2024), you owe taxes on the excess contributions. Contact the plan administrator at whichever job you left first to request a refund of the excess, or you will owe taxes on it twice.

Do I have to report my 401(k) balance on my tax return?

No. You only report contributions and withdrawals, not the account balance. The balance is for your own records and for required minimum distribution calculations after age 73, but it does not go on your tax return.

Can I deduct 401(k) contributions if I am self-employed?

No. Self-employed people use a Solo 401(k) or SEP-IRA instead. Those have different contribution limits and reporting rules. A traditional 401(k) is only available through an employer.

What if my employer made a mistake on my W-2 401(k) amount?

Contact your employer's HR or payroll department and ask them to issue a corrected W-2 (Form W-2c). Once you receive it, file an amended tax return (Form 1040-X) with the corrected amount. Do this as soon as you notice the error to avoid IRS notices.