The $916 million loss that Donald Trump claimed on his 1995 tax returns, reported by The New York Times on Saturday, was a shocking number. But what appalled most people more was what the Times pointed out next: That the high-living Trump could have used the losses to avoid paying taxes over a period of 18 years. Hillary Clinton wasted no time in seizing the chance to score points: “While millions of American families, including mine and yours, were working hard, paying our fair share, it seems he was contributing nothing to our nation,” she said at a campaign rally in Ohio Monday.

For tax experts, the scale of the losses might also have been a shock, but there was nothing surprising or unfair about the idea that Trump could have zeroed out his taxes for years. More than 1 million Americans used the same tax break in 2014, and it's a perfectly legal tax maneuver.

But Trump’s taxes actually do point to a larger unfairness about the system: while Trump has access to that maneuver, poor Americans don't.

The rule he’s using is called “net operating losses,” and it lets businesses offset their profits in boom years with losses in down ones. The larger idea is called “income smoothing”—for companies that might make way more money one year than the next, it lets you average out income over time, so your taxes reflect the amount you earn over the long term.

It’s currently available only for businesses and taxpayers with business income. Trump was able to take advantage of it because he owns businesses, such as limited liability companies and sole proprietorships, whose incomes are passed through onto his personal income taxes. For poor households—which generally don’t have business income, but have wage incomes that can also fluctuate significantly from year to year—this tax maneuver is unavailable.

“It’s a reasonable part of the tax code to let businesses carry forward their losses, because they do have ups and downs, and there’s a business cycle,” said Lily Batchelder, a former economic official in the Obama administration. “But one thing that is unfair about it is that we don’t allow families that have only wage income and not business income to do the same thing.”

For years, this has rankled tax reformers. An ideal tax code would be one that taxes all income equally, no matter how or when it was earned. So just like Trump, a mom-and-pop shop that loses money during a recession and has positive earnings during the ensuing recovery should be taxed on its total profits over time, not dinged for its big profits during boom years.

But this common-sense accommodation is not applied equally throughout the tax code: Individuals who earn money through wages can’t roll over their unused deductions and exemptions to previous or successive years. This doesn’t usually hurt middle-class wage earners much; their income tends to be relatively stable, and high enough to use the full annual deductions they’re entitled to. But it’s a lost opportunity for many low-income taxpayers, whose incomes also can swing widely from year to year—and who may end up leaving money on the table when they don’t earn enough. For instance, a household that earns just $5,000 in a year cannot claim the full standard deduction, which currently is $12,600 for a married couple. If that family earns $30,000 next year, it can claim the full $12,600 standard deduction—but nothing more. Despite the fact that the family’s two-year income was $35,000—enough to claim the combined $25,200 standard deduction over that period—the tax schedule allows it to claim only a standard deduction of $17,600. If they’d been allowed to claim that combined standard deduction, the family could have taken home an additional few thousand dollars.

Or consider the Earned Income Tax Credit, which provides an income boost for low-income workers up to a certain income threshold. A person who earns too much to claim the credit one year but then loses his job and earns nothing the next year will receive no EITC benefits under the current system. Averaged over both years, though, his income may allow him to claim a sizable credit. Just as with the standard deduction, the federal government’s arbitrary decision to calculate taxes annually penalizes this worker.

Batchelder, who now is a professor at New York University, calculated in 2003 that if taxes of low-income Americans were calculated over a longer period of 10 to 25 years—the way Trump gets to do it through his business income—rather than strictly on an annual basis, their tax rate overall would be 2 percentage points lower.

It wasn’t always the case that the poor were denied the chance to smooth out their income to help with their tax burden. Before the 1986 tax reform, individual taxpayers could average their income over time, just like businesses—but that rule was repealed in the name of simplifying the tax code. Before the age of computers and cheap software to help prepare taxes, calculating tax liabilities over many years was far more difficult. Technological improvements have significantly reduced compliance costs since then.

Batchelder doesn’t propose returning to the pre-1986 system of averaging income over time—although she called it interesting—but instead proposes allowing poor taxpayers to “carry back” the standard deduction and personal and dependent exemptions one year. In other words, they could apply the unused deduction and exemptions to a previous year’s income, and thus collect a little more money. Batchelder also proposes allowing taxpayers to average their income over two years in order to calculate EITC benefits. Overall, she estimates that the plan would reduce the penalty from annual taxation by about 75 percent for the poorest taxpayers.

This looks like a conflict between the rich and the poor, but it’s also a conflict between two basic tax principles: fairness and simplicity. It’s harder to average income over years: it requires more record keeping, more calculations, and doesn’t quite seem intuitive. But it’s fairer. The truth is that a good portion of the tax code’s complexity is due to similar tax breaks, arcane measures intended not to benefit a politically connected group but simply necessary to define income in a reasonable way.

“There’s lots of stuff that is hiding in the tax code that people point out, ‘Ah, that’s a loophole,’” said Kyle Pomerleau, director of federal projects at the Tax Foundation. “But really that’s just a way that the tax code defines income.”

Net operating losses do not make the tax code any simpler. But compared to a world without NOLs, it’s actually fairer. The same could be said about Batchelder’s proposed changes to the EITC, standard deduction and personal and dependent exemptions.

Taxes are complicated, and there’s no way around it. If any presidential candidate knows this, it should be the man who most uses these tax breaks and actually understands their purpose: Donald Trump.

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