Most small business owners think of their income as their own. You do the work. You bill the client. The money lands in your account. So when the IRS audits you and says you left income off your return, it feels like a problem that belongs to you alone.

But that is not always how the tax law sees it. If you are married and live in a community property state, the law may treat half of what you earned as belonging to your spouse. That can matter a lot when the IRS comes calling. Half the income could mean half the tax.

So here is the question. If the IRS audits a married business owner in a community property state and finds unreported income, can that owner push half the tax onto the other spouse? And just as important, when does that argument have to be made?

The recent case of Branch v. Commissioner, T.C. Memo. 2026-51, gives us a chance to look at this. The answer turns out to be less about the tax math and more about timing.

The Facts

The taxpayer ran a home care business in New Orleans. The business cared for clients with intellectual and physical disabilities so they could stay out of institutions. It was a real business with real clients. Most of the clients were on Medicaid.

The trouble was simple. The taxpayer did not file income tax returns for three straight years. The IRS noticed. It prepared substitute returns on her behalf and issued a notice of deficiency.

The proposed deficiencies were large. The IRS said she owed tax on more than $2 million of unreported business receipts each year. It also added penalties as additions to tax for failing to file and failing to pay.

The taxpayer did not really dispute that she failed to report the income. Instead she argued that the IRS ignored her business expenses, ignored some itemized deductions, and got her filing status wrong–as it normally does in these situations. There is nothing really noteworthy about those. The interesting piece was an argument she raised about community property. And it shows up at the very end, which is exactly the problem.

Louisiana is a community property state. So are Texas, California, Arizona, and a handful of others. In these states, most income earned during a marriage is owned by both spouses equally. This is the case no matter who actually earned it and regardless of whether you file married jointly or married separately.

The federal tax law follows this. If they do not file jointly, married people who live in a community property state generally each report one half of their community income on their own returns. This is not a new rule. The Supreme Court blessed it decades ago and there is a tax form on the tax returns that provides for the allocation. So if a wife earns $100,000 from her business in a community property state, the tax law may treat $50,000 of that as her husband’s income, taxable and reportable to him.

You can start to see why this matters in an IRS audit. If half of the unreported business income belongs to the spouse, then only half of it can be taxed to the business owner. On a multi-million dollar deficiency, that is a large swing. It can cut the tax bill roughly in half.

There are cases that show this is not always so clean. And the rules get complicated when a couple marries partway through the year or when one spouse earns separate property. But the general rule is real, and it is powerful. So why did it not help here?

When Is It Too Late to Raise the Argument?

This is where the case turns. The taxpayer did raise the community property argument. She said that any income from the business should be split one half to her and one half to her husband. On its face, that is a logical request in a community property state.

The problem was when she said it. She did not raise community property in her petition. She did not raise it at trial. She did not even raise it in her opening brief. It showed up for the first time in her answering brief, which is the last paper filed before the court decides the case.

The U.S. Tax Court has a long-standing practice. It generally will not consider a new issue raised for the first time in an answering brief. The reasoning is fairness. The other side never got a chance to respond or to put on evidence. So the court treated the community property argument as abandoned and decided against her on it.

There was a second problem. And it would have mattered even if the timing were fine. To split the income, the taxpayer needed to show how much of it was actually community income and how much her husband earned. She never put that proof in the record. The court usually will not guess. Without evidence showing what should be allocated to the husband, there was nothing to split. The argument failed on the facts as well as the timing.

The Takeaway

Community property can be a real tool for a married business owner facing an audit in a state like Louisiana or Texas or California. Half of your income may legally belong to your spouse, which can cut a deficiency in a meaningful way. But the law gives you that benefit only if you claim it the right way and at the right time. Raise the argument in your petition (or even in your tax return), not in your last brief. And come with proof of who earned what. The lesson from this case is that a good legal argument made too late is the same as no argument at all. If you are facing an IRS audit of business income, the time to plan your defense is at the start, not the finish.

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