Asked Thursday whether the donation would come from Trump's own fortune or from the coffers of the Trump Organization, Sanders indicated she wasn't sure legally where the donation would originate, but that it would be the President's personal money.
President Trump is pledging $1 million of his own cash toward the Hurricane Harvey relief efforts in Texas.
President Donald Trump is expected to meet with Senate Majority Leader Mitch McConnell, House Speaker Paul Ryan, Senate Minority Leader Chuck Schumer and House Minority Leader Nancy Pelosi on September 6 to discuss the best way to proceed on handling recovery efforts.
Trump has been following through on a campaign pledge not to take a paycheck and instead donate the money; his first donation was to the National Park Service, even as his budget proposed cuts to the Interior Department.More news: Defending champion Kerber beaten by Japanese teenager at US Open
The President has not yet decided where he will donate the money, Ms Sanders said. He has pledged $1 million in personal funds to Harvey relief efforts.
Trump used a similar "reporters decide" gimmick at the beginning of his administration, that time with his presidential salary, which he is declining to accept. Then-press secretary Sean Spicer told reporters at a March briefing that Trump "has kindly asked you all determine where that goes".
"I mean, I've heard $100 billion bantered around - not for a vote next week - but that may be the total amount of some kind of emergency package when it's all said and done".
Trump has been criticized in the past for giving far less of his income to charitable causes than many other multi-billionaires.More news: England v West Indies: Headingley defeat for Root's men
Trump tweeted a statement to storm victims on Wednesday.
Harvey's flood waters have heavily damaged tens of thousands of homes across Texas and killed at least 30 people.
Mr Trump, who also visited hurricane-ravaged Texas earlier this week, is expected to return to the region on Saturday.More news: Tillerson distances himself from Trump's Charlottesville response