Experts say this increase is in large part due to Russian Federation and its illegal annexation of Crimea in 2014, which caught the alliance flat-footed.
He also renewed a demand that they even double that - though many question what they could usefully spend it on.
After a tense first day, Trump didn't ease up on the second.
Trump had spent his time in Brussels berating members of the military alliance for failing to spend enough of their money on defence, accusing Europe of freeloading off the USA and raising doubts about whether he would come to members' defence if they were attacked.
"The people voted to break it up (Britain's ties with the EU)", Trump told a press conference in Brussels on Thursday. "He does not see the value, and does not recognize that the U.S. also benefits from it".
Trump said the best was for the European allies to spend money on defence was to buy United States military equipment.
The U.S. President was also asked if he would be prepared to recognise Crimea as part of Russian Federation after it was annexed from Ukraine by Moscow in 2014.
Sources close to the talks told DW's Teri Schultz that Trump demanded European NATO members meet the alliance target immediately, rather than increase spending gradually as agreed to at a previous NATO summit in 2014. Trump said that would happen over "a fairly short period of time". Trump tweeted this morning before the second day of talks.
As well as Merkel, Spanish Prime Minister Pedro Sanchez and Charles Michel, the prime minister of Belgium, were also singled out by Trump for undershooting on their spending targets when USA taxpayers, funding a defence budget worth about 3.6 percent of their national income, foot much of NATO's bills.
But at the end of the summit, Stoltenberg said the figure was $41 billion, and was contained in a paper published before the summit, which suggests that no new money was going to be committed. "He generally dislikes the Alliance and Allied solidarity, the very principle of an alliance and mulitlareral frameworks", she said.
That would represent a massive upheaval of budgetary priorities in Europe where Germany and many others have pledged only to reach 2 percent by 2024 or later, the report noted.
Trump has berated members of the alliance for failing to spend enough of their money on defense, accusing Europe of freeloading off the USA and raising doubts about whether he would come to members' defense if they were attacked.
Radev said that, on the other hand, Trump was right, because each country should make a contribution, in a world of growing threats, and build effective capabilities. "They're going to up it at levels that they've never thought of before", Trump said. "They've raised an additional $33 billion that's been put up by the various countries, not including the U.S. And the U.S. commitment to North Atlantic Treaty Organisation is very strong".
As the United Kingdom grapples with its own future in the European Union, I hope that President Trump's visit will help to solidify the long friendship between our two great countries.
It was only last month that after a disastrous G-7 summit, Trump signed a joint communiqué with other allies and then changed his mind while flying home.
"We understand your message, but some people ask themselves, will you be tweeting differently once you board the Air Force One?" one reporter asked. "He's been very nice to me". "I'm very consistent. I'm a very stable genius". Why are there only 5 out of 29 countries that have met their commitment?
There, while on board Air Force 1, he used his Twitter feed to rescind his support of a joint communique and slam Trudeau personally after hearing the prime minister repeat Canada's insistence it would defend itself from USA aggression on trade.