Democratic presidential candidate, former New York City mayor Mike Bloomberg speaks to supporters at a rally on February 20, 2020 in Salt Lake City, Utah. George Frey | Getty Images

Unredacted returns, by contrast, offer a lot more insight into a person's finances, if they're combined with other documents such as a statement of net worth. Here are a few areas to key in on if Bloomberg releases an unedited copy of his returns.

Partnership income

Democratic presidential candidate former New York City Mayor Mike Bloomberg delivers remarks during a campaign rally on February 12, 2020 in Nashville, Tennessee. Brett Carlsen | Getty Images

The first two pages of a Form 1040 sum up your taxable income. However, all those data points flow in from the attached schedules that accompany your return. Schedule E, which spells out income or losses from partnerships, S-corporations and rental real estate, would be a highlight of the billionaire's return. That's because income he receives via Bloomberg LP, the giant financial data and media company, would be reported there. The billionaire owns 88% of the business, according to Forbes.

Knowing Bloomberg's share of income from the business could give some insight into income generated by the partnership, Nitti said. "If we get a Schedule E that shows income from Bloomberg LP, people will zero in on it," he said. The tax returns for the company itself would be even more telling — if they were released. "Schedule E only refers to his deductions and flow-through income," said Ryan Losi, CPA and executive vice president of Piascik, an accounting firm in Glen Allen, Virginia.

Foreign account reports

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When Bloomberg shared the redacted details of his 2012 finances, journalists found out he held money in accounts in Hong Kong, Paris, London and Bermuda, according to the Journal. If the presidential candidate still holds funds overseas, he'll need to file a report of Foreign Bank and Financial Accounts, or FBAR, with the Treasury Department's Financial Crimes Enforcement Network. Americans are required to submit a FBAR if they have an interest in or signatory authority over at least one account outside the U.S., and the aggregate value of all the foreign accounts exceeded $10,000 at any time in the year. There's a $12,921 penalty for non-willfully failing to file, while individuals who flout the law could face fines of up to $129,210 or 50% of the account.

"The FBAR will tell you where the cash is stashed, the type of account and the maximum value of the year," said Losi. "Meanwhile, the income tax return will only show you the interest, dividends and capital gains derived from those accounts — not the actual values," he said. Further, citizens who submit a FBAR may also need to turn in Form 8938 to the IRS. This "statement of specified foreign financial assets" is attached to taxpayers' income tax return. Taxpayers have until April 15 to file a FBAR, but they get an automatic six-month extension if they miss the deadline. Meanwhile, Form 8938 is due with your return.

Charitable giving

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Individuals who take itemized deductions, including tax breaks for charitable giving, spell out their write-offs on Schedule A. Gifts by cash or check are straightforward, but gifts of appreciated stock, real estate and other property require taxpayers to fill out Form 8283, which details noncash contributions. What we might see on Bloomberg's 1040 is the amount of money that goes to Bloomberg Philanthropies, his charitable giving initiative, said Nitti.