Pre-Tax Contribution

There are two routes. A payroll deferral to a traditional 401(k), 403(b), governmental 457(b) or TSP never enters your taxable wages. IRS Topic 424 explains that elective deferrals are left out of box 1 of your W-2, shown in box 12 for information, and not subject to income tax withholding. They are still wages for Social Security and Medicare, so FICA tax is due on them as usual.

A deductible traditional IRA contribution works through your tax return instead. You contribute money that was already paid to you, then deduct it, which lowers your adjusted gross income. If you or your spouse is covered by a workplace plan, the deduction phases out as income rises: for 2026, between $81,000 and $91,000 of modified AGI for a covered single filer and between $129,000 and $149,000 on a joint return where you are covered. Above the range the contribution is nondeductible, and its basis must be tracked on Form 8606.

Benefits paid for by salary reduction through a cafeteria plan go further. HSA contributions made this way, health FSA contributions and health premiums paid through the same plan escape both income tax and payroll tax, so they also save the employee’s 7.65% Social Security and Medicare tax, or 1.45% on pay above the $184,500 Social Security wage base for 2026. Employer matching and profit-sharing contributions are pre-tax too, and they aren’t counted as wages for Social Security or Medicare.

The saving is your contribution times your marginal tax rate, federal plus state, not your average rate. A $10,000 deferral by someone in the 22% federal bracket cuts federal income tax by $2,200, so take-home pay falls by $7,800 before any state saving. The same deferral saves $1,200 in the 12% bracket and $3,200 in the 32% bracket, so it is worth most in your highest-earning years.

Because a 401(k) deferral, like most retirement-account contributions, never enters adjusted gross income, and a deductible IRA contribution is subtracted in reaching it, pre-tax saving also lowers the income that many other rules read. A lower AGI can make you eligible for the Saver’s Credit, which for 2026 disappears above $80,500 of AGI on a joint return and $40,250 for single filers. A lower MAGI can also enlarge a marketplace premium tax credit or bring you under the Roth IRA contribution phase-out.

A Roth 401(k) or Roth IRA contribution is the mirror image: no deduction now, tax-free withdrawals later. If your tax rate is the same at both ends, the two come out identical, because the order of multiplication doesn’t matter. A $10,000 pre-tax contribution that doubles and is then taxed at 22% leaves $15,600. A $7,800 Roth contribution, which costs the same take-home pay, doubles to $15,600 tax-free.

So the decision turns on one comparison: your marginal rate now against the rate you expect when the money comes out. Pre-tax tends to win in high-earning years followed by a lower-income retirement. Roth tends to win early in a career, in a low-income year, or when later income will be pushed up by pensions, Social Security and required withdrawals from a large pre-tax balance.

Many households split the difference for tax diversification, keeping both kinds of money so each retirement year can draw from whichever is cheaper. One rule takes the choice away: starting in 2026, workers whose prior-year FICA wages from their employer topped $150,000 must make workplace catch-up contributions as Roth.

Pre-tax money is taxed only once, on the way out. Its growth isn’t taxed while it stays in the tax-deferred account, but every withdrawal, growth included, is ordinary income in the year you take it, at whatever rates apply then. Before 59½ most withdrawals also face a 10% additional tax unless an exception applies. From age 73, or 75 for people born in 1960 or later, required minimum distributions force a growing share out each year whether you need it or not.

A pre-tax balance therefore overstates what you own. A $500,000 traditional 401(k) might be worth $400,000 or less after tax, depending on the rates at which it comes out. Heirs don’t get a step-up in basis on it either: inherited pre-tax money is ordinary income when they withdraw it, and most non-spouse heirs must empty the account within ten years.

This is why pre-tax saving and Roth conversions often appear in the same lifetime plan. The deduction is taken in high-earning years, and part of the balance is converted later, in low-income years before RMDs begin, at a lower rate than the contributions saved.

Most mistakes come from misreading what the tax break does. A workplace deferral cuts income tax but not payroll tax, and the tax it saves is postponed, not forgiven, so the rate at withdrawal decides whether it paid off. The rest are about limits, records and payroll routes, which matter most after a job change or when you save in more than one tax-advantaged account. A few to check at enrollment and again before year end: