In the absence of publicly released tax returns, the line highlighted in yellow below may offer the most insight into how much money Donald Trump actually earns each year.

Crain's New York dug up Trump's quarterly property tax bill from the city of New York, from which that snippet is taken. He owes about $97,000 by July 1, if he hasn't already paid it, or about $192,000 in total. That large figure is nonetheless about $304 less than it wouldn't have been without the "Basic STAR - School Tax Relief" credit for which Trump was eligible.

What's interesting about the STAR credit, though, is that there's an income requirement that applies. In order to be eligible for the basic version, you must meet three qualificiations: You must own your own home, it must be your primary residence, and you and your spouse can't have an annual combined income of more than $500,000. There's an "enhanced" STAR credit, too, with an income limit of $84,550 and a required age of at least 65 (which Trump meets). This suggests that Trump's income in 2014 (the applicable year) was between $84,550 and $500,000 -- somewhat more modest than you might have expected.

Earlier this year, Crain's looked at Trump's 2015 filing and found the same credit. In fact, he received it from 1999 through 2009 and from 2014 on. (In 2011, the state introduced the $500,000 limit, using income from the 2009 tax year.) When asked by Crain's, the Trump campaign insisted that his receipt of the credit was a mistake -- and a spokesperson for the city agreed that the credit had been mistakenly applied.

But earlier this month, the credit re-appeared.

What we do know about Trump's stated income is sketchy. Last month, The Post reported that Trump tax filings from the late 1970s showed that the businessman's income was zero. Those returns were made public during a legal proceeding and appear to be the only such returns that have come to light. Trump has refused to release more recent filings, arguing that the returns are under audit and therefore his lawyers think he should keep them private. (We spoke with tax attorney Steven Goldburd, who agreed.) Asked to prove that his filings were under audit, Trump released a letter from his attorneys suggesting that the audit applied to his returns from 2009 on -- meaning that those from earlier could potentially be released. Trump has refused to do so.

Trump's house. (AP Photo/Mark Lennihan, File)

So what's going on here? Is this a continued failure of bureaucracy? Or is it the case that Trump actually earned less than $500,001 in 2014?

It could be the former. "There is supposed to be a clerical check for income over $500,000," tax attorney Goldburd wrote when we reached him again by email on Monday. "However, things like this are often overlooked. When dealing with the government, anything is feasible."

Trump has released personal financial disclosure documents for his candidacy which detail a great deal of wealth, much of which is in the form of real estate holdings. (That's different than income, of course, which is the amount of money Trump is earning each year.) And that real estate could be the key to the question.

Goldburd pointed out that it's hard to know how Trump might have come in under the $500,000 limit. It's possible, he said, that Trump "could have sold interest in a partnership or a building that he was not actively involved in (passive income), which would have released 'suspended losses' from prior years which would only be allowable after sale." In other words, that he could have taken a step that resulted in his taking a big loss that, when combined with his annual income, reduced that income below the $500,000 mark.

Or he may have seen less income thanks to depreciation. We explored this a bit in March, looking at how tax law mandates that the value of a property decrease each year. That's its depreciation -- and the amount of the depreciation is a loss to the property owner. Here's how we described it at the time.

Let's say you buy a building for $10 million. Every year, the value of that property depreciates. Say it depreciates $1 million a year. (The IRS mandates such a depreciation schedule.) After year one, it's worth $9 million. After year two, $8 million, and so on. After nine years, it has depreciated $9 million. If it were sold at that point for more than you paid -- say, $11 million -- you'd pay taxes on the $10 million difference between the $11 million you got and the $1 million value to which it had depreciated.

But there's benefit! That $1 million a year counts as a loss. So if you make $10 million a year in income, but also own 10 properties that are each depreciating at $1 million a year, your income and your losses are equivalent. Boom. No net income, no income tax.

And on top of that, you put yourself in the running for the STAR tax credit. No matter how much Trump may have made from "The Apprentice" in 2014, for example, his real estate holdings could have dropped his net income to less than $500,000.

The whole point here is we don't know what's happening. Without Trump releasing his tax documents, we're left to speculate about how much he earns and how he earns it. We don't know if the STAR credit is a function of Trump's savvy tax maneuvers or if it's a function of New York's tax department repeating the mistake of giving away money for three years in a row.

Trump can answer that question easily by releasing his tax returns. That he chooses not to leaves us to speculate on particular line items in quarterly tax documents from the city where he lives.