Updated 2026-03-30
401(k) Tax Guide
Understanding how your 401(k) is taxed at every stage
Your 401(k) has different tax implications at contribution, growth, and withdrawal. Understanding these rules helps you minimize your lifetime tax burden and keep more of your retirement savings.
Contributions and Your W-2
Traditional 401(k) contributions reduce your taxable income (Box 1 on W-2) but are still subject to Social Security and Medicare taxes (Boxes 3 and 5). Your contributions appear in Box 12 with code D. Roth contributions appear with code AA and do not reduce taxable income.
Tax Treatment by Account Type
| Stage | Traditional 401(k) | Roth 401(k) |
|---|---|---|
| Contributions | Pre-tax (reduces W-2 Box 1) | After-tax (no deduction) |
| Investment Growth | Tax-deferred | Tax-free |
| Qualified Withdrawals | Taxed as ordinary income | Tax-free |
| Early Withdrawal Penalty | 10% + income tax | 10% on earnings only |
| RMDs Required? | Yes, at age 73/75 | No (SECURE 2.0) |
| W-2 Box 12 Code | D | AA |
Withdrawal Taxes
Traditional 401(k) withdrawals are taxed as ordinary income. There is a mandatory 20% federal withholding on distributions. If you withdraw before age 59 1/2, you may owe an additional 10% early withdrawal penalty. State taxes also apply based on your state of residence at the time of withdrawal.
1099-R Form
Any 401(k) distribution triggers a 1099-R form. Box 7 contains the distribution code: code 1 (early distribution with penalty), code 2 (early distribution, exception applies), code 7 (normal distribution age 59 1/2+), code G (direct rollover). Keep this form for tax filing.
Frequently Asked Questions
No. Traditional 401(k) contributions reduce federal and state income tax, but they are still subject to FICA taxes (Social Security at 6.2% and Medicare at 1.45%). Your Social Security benefit calculation includes your full pre-contribution salary.
Direct payments from a 401(k) have a mandatory 20% federal income tax withholding. This is not the actual tax owed - it is just withholding. Your actual tax depends on your total income and tax bracket. You may owe more or get a refund when you file.
You cannot avoid taxes on Traditional 401(k) withdrawals entirely, but you can minimize them. Strategies include: Roth conversions during low-income years, spreading withdrawals across years to stay in lower brackets, and contributing to Roth 401(k) for future tax-free income.
Pavlo Pyskunov
Managing Director & Investment Fund Director
Pavlo Pyskunov analyzes employer-sponsored retirement plans using IRS publications and DOL Form 5500 filings, helping workers maximize their 401(k) savings through data-driven guidance.
Last updated: 2026-03-30