What to expect in Romney's tax return

Mitt Romney's 2010 tax return will offer up some new information about his finances. But it won't paint a complete picture.

NEW YORK (CNNMoney) -- What can the public -- and his rivals -- expect to learn when Mitt Romney releases his 2010 tax return on Tuesday?

Interest is high, largely because of Romney's vast wealth: He leads the Republican field, and President Obama, by a mile in that category.

His 2010 tax return, which he'll post online along with an estimate of his 2011 tax liability, will offer up some information not previously made public.

But his return will probably leave many unanswered questions about the extent of his holdings and how much he has profited from his retirement package from Bain Capital, the private equity firm he founded.

His income: For the first time, Romney will reveal his 2010 income. And the number is likely to be big, since his net worth is estimated to be as high as $264 million.

Among other things, his return should reveal how much he earned in speaking fees and from his book, No Apology: The Case for American Greatness.

But the majority of his income will come from an extensive portfolio of investments.

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Of particular interest will be how much he made from so-called carried interest, which is taxed at the preferential rate of 15% and is reported as a capital gain.

Carried interest is compensation paid to general partners at private equity firms -- such as Bain Capital, which Romney left in 1999.

General partners manage the firm's investments. If those investments are sold at a profit, the carried interest represents a portion of those profits above a minimum rate of return.

Romney's retirement package entitled him to receive income from Bain's work, according to his financial disclosure form on file at the Federal Election Commission.

It's not clear, however, how much light his 2010 tax return will shed on the carried interest he made, since it may simply be wrapped into the other capital gains he reports.

If Romney withdrew any money from tax-deferred accounts, such as his IRA, his return would show how much he withdrew and if he incurred any penalty for an early withdrawal.

Romney's taxes - George Romney

Likewise, any taxable income he made from investments in his blind trust -- or his wife's -- would show up as well, although the return would not likely show the actual sources of that income, said Roberton Williams, senior fellow at the Tax Policy Center.

His tax liability: How much Romney paid to the IRS will also be news -- as, of course, will be his effective tax rate.

Romney said last week that his effective tax rate was 15%.

But it may be even lower than 15% if, for instance, Romney had a lot of deductions, which could offset a sizeable chunk of his tax liability.

In addition, his rate may be lower still because his return may understate his income. Here's why: He may not have to report some forms of tax-free income -- such as gains from the sale of a home up to a cap, said Mark Luscombe, principal federal tax analyst at tax information publisher CCH.

(The same is true of his rival Newt Gingrich's effective tax rate.)

On the other hand, his effective rate might be somewhat higher than 15% if a lot of his taxable investment income was generated by holdings that were bought and sold within a year. In that case, his investment income would be taxed at ordinary income tax rates, and probably all of it at his top rate of 35%.

His deductions: Romney almost certainly itemizes his deductions -- meaning he has enough eligible items to deduct that, when combined, exceed the value of the standard deduction.

Among the itemized deductions he's likely to claim are charitable contributions. Romney, a Mormon, told Fox News on Sunday that he regularly tithes 10% of his income to the Mormon church.

And here's another prediction: He is likely to deduct high fees for help preparing his tax returns, since Romney's 1040 almost certainly will not be a TurboTax affair.