Mr Trump said that NATO would soon discuss member defence spending at a higher level than the alliance's target of 2% of GDP.
"I think 4% is the right number," he said.
The US President insisted NATO leaders were now "putting up a lot" and it was "unnecessary" to pull the US out of the organisation.
He said Germany had agreed to increase "very substantially" the timescale for increasing funding.
"The people have stepped up today like they have never stepped up before," he said.
Mr Trump said everybody in the room had thanked him, including NATO Secretary General Jens Stoltenberg, and described himself as a "very stable genius".
He then claimed that the Secretary General gave him "total credit" for securing additional funding agreements for the alliance.
All NATO nations will be up to 2% on defence spending over a "relatively short period of years", he said.
Earlier, Mr Trump said alliance countries were not spending "nearly enough" on defence - despite billions of additional dollars being invested since he issued a warning over the US' future contribution to the alliance.