It’s all about tax rules that require you to depreciate, or reduce, the value of buildings over time, even if the market value of the structures is going up. If your depreciation is greater than your traditional income from work and businesses, Congress lets you report negative income. If these paper losses are just a dollar more than traditional income, it wipes out your income taxes for the year.

If Trump’s returns show he has paid no income taxes in some years, that could be a reason he has not yet released details.

Congress says most Americans can deduct no more than $25,000 of real estate depreciation against their income. But if you work two days a week managing real estate and own enough that the depreciation exceeds your salary and other income, Congress lets you live income-tax-free. And for as long as you keep buying buildings and depreciating them, the tax does not come due.