The GOP tax law, which lowered the federal corporate rate from 35 percent to 21 percent, is a "huge tailwind" for American businesses, Buffett said.
"It certainly means corporations will pay quite a bit less in tax than they otherwise would," he said. "When we make money in 2018 domestically, and subject to a lot of little things here and there, basically we'll be paying at 21 percent instead of 35 percent. That's a lot of money."
The 87-year-old Berkshire chairman and CEO released his annual report to shareholders on Saturday. It revealed that the company's net worth increased to $65.3 billion for the 2017 tax year, including $29 billion because of tax reform.
In a "Squawk Box" interview, Buffett explained the reasons for most of the gain.
"[First,] we had about $100 billion of unrealized gain in equities. When they're sold you pay tax on that. And previously when the tax was 35 percent we would have had a $35 billion reserve for taxes against that as a liability. That would drop to about 21 billion," he said. "So $14 billion, roughly, was a reduction in the amount of tax that when we sell those securities we will pay. It wasn't cash now. But it reduced a liability. When you reduce a liability net worth goes up."
"The other important point related to the same thing, deferred income taxes, [is] when we buy some kind of fixed asset," he said. "It's particularly a tailwind if you've got ... lots of deprecation and taken bonus deprecation upfront. So it's a big item there."
However, Buffett made a point to say the money is not in the bank yet: "We haven't really gotten cash yet from this. But we will save cash as we go along."
In his letter, Buffett also said the Omaha-based conglomerate has amassed a $116 billion war chest to spend on a deal, but he feels prices were too high to act in a big way last year.
Buffett has long been against lowering taxes, especially for wealthy Americans like himself. In October, he told CNBC the old corporate tax rate was not hurting American businesses in the world economy.
But he said at the time that he hoped the corporate tax rate would be lowered. "I would like it in the sense that it would be good for a million shareholders of Berkshire in terms of their returns."
Buffett was a supporter of Democrat Hillary Clinton in the 2016 presidential election. But he's since said he hopes President Donald Trump has a successful administration and positive effect on the economy. "
Buffett, also nicknamed the "Oracle of Omaha" for his successful track record of stocks picks and his market commentary that's widely followed by the investment community, joined CNBC from Omaha, Nebraska. He became the controlling shareholder of Berkshire in the 1960s.
He also spoke on these topics in the CNBC interview:
— Stocks vs bonds, 'I would choose equities in a minute'
— 'We've bought more Apple than anything else' in the last year
— Buffett sees buybacks as an option if Berkshire can't find ways to deploy its big cash stockpile
— There are three ways to go broke: 'liquor, ladies and leverage'— I don't think Berkshire should avoid doing business with people who own guns
— Bezos, Dimon, and I aim for something bigger on health care than just shaving costs
— Buffett will tell you which is better, Taco Bell or Chipotle, when they start serving burgers
— March Madness contest will double the payout if a Nebraska team wins it all