Corey Lewandowski also told CNN that the plan will be published on Trump's website.
On Wednesday, Trump said his plan will call for middle class tax cuts and hikes for hedge fund managers.
"(It) will be very long on policy and will be a great plan, with a major reduction in taxes for the middle class," Trump said at a town hall meeting in Columbia, South Carolina, at the University of South Carolina.
Trump promised that his plan would be "great" for middle income residents and businesses, but not so much for hedge fund managers, who he has turned into political punching bags of late.
"It's going to be very specific," Trump said of his proposal. "And I think it's going to be a plan that creates incentives, and I think it's going to be a plan that makes people happy, other than maybe the hedge fund guys, who make hundreds of millions of dollars and pay very little tax. I mean, those guys will not exactly love me."
Earlier in the evening on Wednesday, Trump blasted the head of Turing Pharmaceuticals, Martin Shkreli, who catapulted into the spotlight this week after a New York Times report revealed he raised the price of a pill from $13.50 to $750.
"He looks like a spoiled brat to me. You want to know the truth? He looks like a spoiled brat," Trump said Wednesday.
Then he noted that Shkreli was a hedge fund manager before he took over Turing.
"And he's a hedge fund guy, and as you know they're the only ones I'm raising taxes on, they're going to be paying up," he said.