NEW YORK (CNNMoney) -- Billionaire investor Warren Buffett this week showed a little more leg in his campaign to get Congress to raise taxes on the uber-rich.

In a letter to Republican Rep. Tim Huelskamp Tuesday, Buffett revealed that his adjusted gross income last year was $62,855,038 and that his taxable income was $39,814,784. Buffett said he paid $15,300 in payroll taxes.









Buffett also said his federal income tax bill came to $6,923,494, or 17.4% of his taxable income -- two points he revealed in a New York Times op-ed in August urging Congress to tax the wealthy more.

Buffett provided a copy of his correspondence with Huelskamp to CNNMoney's Poppy Harlow.

He said in an interview that the roughly $23 million difference between his AGI and taxable income was due largely to deductions he took for charitable giving and local taxes.

Two key reasons he only paid 17.4%, however, is because a lot of his income came from investments, which are taxed at a lower rate than wages, and because payroll taxes are assessed only on wage income.

"People who make money with money are getting taxed at a far lower rate than people who make money by their own labor," Buffett told CNNMoney.

In his letter, Buffett also repeated his offer to release his full tax return if other super-wealthy taxpayers -- like News Corp. (NWSA, Fortune 500) chief Rupert Murdoch -- did the same.

"If you could get other ultra-rich Americans to publish their returns along with mine, that would be very useful to the tax dialogue and intelligent reform," Buffett wrote.

Buffett, chairman of Berkshire Hathaway (BRKA, Fortune 500), also aimed to dispel any doubts that he has not been recounting his income figures accurately.

If other wealthy taxpayers offered to release their returns, Buffett said, he would agree to "a pre-release wager" with anyone for any sum "that the figures in my return will be exactly those used in my op-ed piece."

After the release of the letters, Huelskamp said that Buffett's disclosure, while it may be accurate, is incomplete.

"By sheltering millions of dollars of income from taxation through charitable giving, Mr. Buffett demonstrates that he doesn't trust Washington with his own money either," Huelskamp told CNNMoney.

Huelskamp originally asked Buffett to release his federal tax return because "it is my firm belief that if your name is lent to a national policy and your story the justification for a major overhaul of the tax code, then the American people have a right to see the evidence guiding that policy."

The rule would ensure that people making more than $1 million pay a higher percentage of their income in federal income and payroll taxes than those who make less.

That would be a lot less straightforward than it sounds, however.

And just in terms of averages, the current tax system already satisfies the Buffett Rule. Americans on average pay 16% of their total income in federal income and payroll taxes, while millionaires pay an average of 20.1%, according to the Tax Policy Center.

--CNNMoney's Poppy Harlow contributed reporting to this article.