401k and Taxes Explained

Traditional 401(k): Reduce Taxes Now, Pay Later

A traditional 401(k) contribution is pre-tax — it reduces your taxable income in the year you contribute. The tax benefit is immediate and predictable.

How it works for a $75,000 earner in the 22% bracket:

- Without 401(k): taxable income = $60,000, federal tax = $8,115

- With $10,000 traditional 401(k): taxable income = $50,000, federal tax = $5,915

- Tax savings: $2,200/year ($183/month)

- Net cost of a $10,000 contribution to you: $7,800 — the government contributes $2,200 via avoided taxes

When funds are withdrawn in retirement:

Withdrawals are taxed as ordinary income in the year you take them. If you're in the 12% bracket in retirement (which many retirees are), you pay only 12% on withdrawals — having deferred 22% tax during your working years. That's the traditional 401(k) tax arbitrage: pay tax later at a potentially lower rate.

Required Minimum Distributions (RMDs)

Starting at age 73, the IRS requires minimum annual withdrawals from traditional 401(k) accounts per IRS guidelines. Failure to take the required RMD triggers a 25% excise tax on the amount that should have been withdrawn. This is a meaningful planning consideration for workers who won't need retirement income immediately — Roth accounts have no RMD requirement during the owner's lifetime.

Roth 401(k): Pay Taxes Now, Withdraw Tax-Free

Roth 401(k) contributions come from after-tax dollars. No immediate deduction, no upfront tax savings. But qualified withdrawals in retirement — after age 59½ with the account open at least 5 years — are entirely tax-free, including all investment gains.

Same $75,000 earner, Roth contribution:

- $10,000 Roth 401(k) contribution (after-tax)

- No immediate tax savings — you pay the full 22% on that $10,000 today

- Taxable income remains $60,000

- In retirement: $10,000 plus decades of growth withdrawn completely tax-free

The Power of Tax-Free Growth — in Real Numbers

Invest $10,000 in a Roth at age 30. At 7% annual return over 35 years, that grows to $97,000 by age 65. The $87,000 gain:

- Traditional 401(k): taxed at your retirement bracket — potentially $10,440–$23,490 in taxes

- Roth 401(k): $0 in retirement taxes, all $97,000 is yours

Roth 401(k) RMD Rule Change (SECURE 2.0)

Starting in 2024, Roth 401(k) accounts are no longer subject to Required Minimum Distributions during the owner's lifetime — matching the longstanding Roth IRA rule. This makes Roth 401(k) an even more compelling option for younger workers who want maximum flexibility in retirement.

2026 Contribution Limits: 401(k), IRA, HSA

Traditional vs. Roth 401(k): How to Decide

The classic rule: choose traditional if you expect to be in a lower tax bracket in retirement; choose Roth if you expect to be in a higher bracket later. Simple principle, nuanced application.

Arguments for Traditional 401(k):

- You're currently in the 22%+ bracket and realistically expect to retire in the 12% bracket

- You need to reduce current taxable income to avoid a higher bracket, qualify for a tax credit, or reduce an income-based student loan payment

- You're older (50+) and have less time for tax-free growth to compound into a meaningful Roth advantage

Arguments for Roth 401(k):

- You're early-career and in a low bracket (10%–12%) that will almost certainly rise

- Tax rates broadly are historically moderate and may rise legislatively

- You want tax diversification in retirement — not all your savings in pre-tax accounts

- You don't want to deal with RMD planning

- You have significant expected Social Security income, which can push your retirement tax bracket up

The Decision Point Most People Miss

If your combined federal + state marginal rate exceeds 25–27%, traditional almost always wins mathematically. Below 20%, Roth is typically better. In the 20–27% range, the right answer depends on your specific retirement income projections.

The Practical Advice for Most Workers:

Contribute at least enough to your traditional 401(k) to capture the full employer match — that's a guaranteed 50–100% instant return that nothing else offers. Then consider Roth for additional contributions if you're in the 12% bracket or believe tax rates will rise over your working life.

How 401(k) Contributions Show on Your Paycheck

Your 401(k) contributions appear on your pay stub and your W-2 in specific, standardized ways — and understanding the difference between them helps you catch errors.

On Your Pay Stub:

- "401(k)" or "RETIREMENT" deduction line showing the per-paycheck contribution amount

- This amount is subtracted from gross wages before federal and state income tax is calculated

- FICA (Social Security + Medicare) is calculated on wages BEFORE 401(k) deductions — so traditional 401(k) contributions do not reduce your FICA taxes

On Your W-2 at Year End:

- Box 12, Code D: Your traditional 401(k) contributions (tax-deferred)

- Box 12, Code AA: Your Roth 401(k) contributions (after-tax)

- Box 1 (Wages): Your wages MINUS traditional 401(k) contributions — this is what's reported to the IRS as your taxable income

- Box 3 (Social Security wages): Your FULL wages including any 401(k) contributions — FICA doesn't care about retirement contributions

This is why Box 1 and Box 3 on your W-2 often show different numbers. If you contributed $10,000 to a traditional 401(k) and earned $75,000, Box 1 shows $65,000 but Box 3 shows $75,000. Both are correct — they're measuring different things.

Frequently Asked Questions