Retirement accounts and trading money

A deferral is not a write-off

A pre-tax 401(k) contribution never appears as a deduction anywhere on a return. The money simply never enters box 1 of the W-2. The IRS puts it this way: elective deferrals are “not subject to income tax withholding at the time of deferral” and are not reported as wages, because they are not included in box 1 IRS Topic 424.

Two consequences follow, and both cut against the usual framing.

• Social Security and Medicare are charged anyway. The IRS states that elective deferrals “are included as wages subject to Social Security (FICA), Medicare, and federal unemployment taxes (FUTA)” IRS 401(k) guide. So a deferral does not reduce payroll tax at all.
• It is a delay, not a forgiveness. Pre-tax money is taxed as ordinary income when it comes out. The bet is that your rate later is lower than your rate now, and that is a bet, not a saving.

And a Roth deferral reduces this year's taxable income by exactly nothing. That is the point of a Roth. If someone recommends one as a write-off, they have the wrong account.

You cannot deposit a windfall into a 401(k)

This is the part that ends the idea. A 401(k) elective deferral is a salary-reduction arrangement: in the IRS's own description, “an employee can elect to have the employer contribute a portion of the employee's cash wages to the plan on a pre-tax basis” IRS 401(k) guide. The money moves from payroll to the plan. There is no deposit slip. You cannot write your plan a cheque out of a win.

The only mechanism that exists is indirect, and it is worth knowing because it is real: raise the payroll deferral percentage and live on the win instead of the paycheque for a while. The win is still taxed as whatever it is. What changes is that more of the wages go into the plan. Whether that is a good idea for you is a question for somebody who can see your whole return.

The compensation trap, which almost nobody mentions

An IRA contribution requires taxable compensation. The IRS's own definition is short: compensation is “what you earn from working” IRS Pub 590-A, and the published limit is the annual dollar figure “or if less, your taxable compensation for the year” IRS IRA limits.

Winnings are reported as other income, not as wages and not as self-employment earnings, so they do not meet that definition. A person whose entire year's income is a win, with no job, has an IRA limit of $0, not $7,500. A contribution made anyway is an excess contribution with its own penalty.

How we got there This one deserves its reasoning shown, because it is a conclusion rather than a quotation. The IRS's “what isn't compensation” list does not name gambling winnings. The conclusion is built from the affirmative definition plus where the income is reported. We are stating it that way rather than putting words in the IRS's mouth, and it is the kind of thing to take to a professional rather than to a website.

Two situations change the answer and are worth naming: a married filer can rely on a spouse's compensation, and activity that rises to a trade or business produces net earnings from self-employment, which is compensation. That second one is fact-specific, contested, and not something this page can decide for anybody.

The 2026 numbers, from the IRS

IRS IR-2025-111 IRS Notice 2025-67. Income phase-outs apply to Roth contributions and to deducting a traditional IRA contribution when a workplace plan covers you; the figures by filing status are in the IRS release. We are not reproducing them here, because a phase-out is where a number gets applied to a person and that is the line this section does not cross.

Note the last row of the table carefully. The IRA figure is a ceiling, not an entitlement. The real limit is the lower of that number and your compensation, which is the whole of the section above.

What is actually available

Stripped of the folklore, the honest list is short.

• Raise the payroll deferral and live on the win. The only route from a windfall into a 401(k), and an indirect one.
• Contribute to an IRA up to your compensation, if you have any. Wages from a job count. Winnings do not.
• A spouse's compensation can support a contribution on a joint return.
• Everything else is a taxable account, which is where the protected money sits, and where we say plainly that we are not the right people to take that from.

What this page will not do is tell you whether any of it applies to you. Contribution room, phase-outs, filing status and the rest of your return all bear on it, we cannot see any of them, and a website that pretends otherwise is guessing. Back to after a big win.