Over the years, it has become a tradition for presidential candidates in the United States to release their tax returns in the name of transparency and to convince voters they are honest about their incomes and lifestyles. But as with many election traditions, Donald Trump has so far bucked this trend.

The presumptive Republican nominee has said throughout the primary season that he won’t release his returns because he’s being audited by the IRS. Then Trump told the Associated Press Tuesday that he would not release his tax returns before the election unless the IRS audit wrapped up, saying “there's nothing to learn from them,” and he doesn’t think voters are interested. But after Mitt Romney — who also initially avoided releasing his tax returns when he ran for president in 2012 — called out Trump in a Facebook post Wednesday afternoon, Trump reversed himself, telling Fox News he would release his taxes before the November elections.

Though Trump may be right that the average voter is not very concerned about the details of his tax returns, many have pointed out that he is very much wrong that “there’s nothing to learn from them.” Trump has made many claims about the size of his wealth, his charitable giving and his branded empire, all of which his tax returns would provide information about. Many have speculated about what could be in Trump's tax returns, but Timothy O'Brien at Bloomberg View wrote recently that he saw Trump's tax returns years ago as part of a lawsuit, and there are a number of insights to be gained. Here are some of the areas that we could learn about from looking at Trump’s tax returns:

1. His income: Trump often brags about how much wealth he has, and he has made his rich-guy persona a central piece of his presidential campaign, telling voters he cannot be bought and that they should trust him because he’s done so well in business. But many have raised questions about how much he is actually worth. In March, Fortune dug into his financial disclosures with the Federal Election Commission and found that “Trump appears to have overstated his income, by a lot.”

His tax returns likely won’t provide a full picture of his fortune, but income is the most fundamental factor in a person’s wealth. If the public is able to see his tax returns, we will find out a lot more about whether he comes close to the “more than $10 billion by any stretch of the imagination” that Trump has said he is worth.

2. His Tax Game: The Donald once said that “nobody knows more about taxes than I do — maybe in the history of the world,” so seeing how he much he pays in taxes and what kind of tax planning Trump is involved in could be very informative. Depending on how much income he has, Trump might not pay very much in taxes, especially because he could have used real estate depreciation provisions in the tax code and carried forward business operating losses from past years, Fortune noted.

The Panama Papers have brought a lot of attention to the issue of how politicians and business leaders sometimes use shell companies to hide part of their wealth and avoid paying taxes. If Trump released his tax returns, the public would be able to see whether he has used similar practices.

3. His Business Activities: The Trump Organization and the brand of Trump’s name are very important to him. The billionaire has said his personal brand is worth billions and often touts how important his name is when talking about his wealth, so this is another area where the taxes could provide some fact checking. A look at the mogul’s tax returns, Bloomberg noted, would reveal details about how active his businesses are around the world and give a better sense of the size of his brand.

4. His Charitable Giving: Trump has said he likes to give generously to charities; but like other aspects of his financial life, it’s been difficult for journalists to pin down how much he has given. This is an area that would be significantly cleared up by looking at Trump’s tax returns.

5. His Lifestyle: More loose than his income or his charitable giving is the air of wealth around Trump’s lifestyle. He likes to be seen on yachts and planes and seems to have a taste for the ostentatious. But his taxes could give important clues into which aspects of his lifestyle get written off as business expenses. The tax returns would likely include deductions for categories such as travel, meals and other areas that could be analyzed to provide a window into the world of Trump.

Beyond all of the specific information about Trump that could be learned from his tax returns, he is running for the highest office in the country, and many politicians have said he should simply release the taxes as a matter of principle.

Democratic front-runner Hillary Clinton has been releasing her tax returns for years and has recently mocked Trump for not releasing his own.