Cameron ruffled feathers going into the summit with sabre-rattling on the ￡3.1 billion (US$4.7 billion) annual UK rebate from the budget won in 1984 by Margaret Thatcher.
Diplomats even accused Cameron of taking the summit hostage.
However, the British leader argued he had fended off attempts to whittle down part of the rebate.
“In this town you have to be ready for an ambush at any minute,” Cameron said, adding that accounting changes in how the rebate is calculated could have cost Britain ￡1.5 billion.
By contrast, EU diplomats insisted it was only a technical issue at the summit and the changes affected only 50 million euros at most.