The nation’s big banks have built record profits on the back of home-buyers, lifting their margins on mortgages to the highest level this century.


Research by the Reserve Bank shows an increase in mortgage rates and a reduction in interest offered on deposits are boosting banks’ bottom lines.


The big four banks – ANZ, NAB, Westpac and the Commonwealth Bank –  reported a combined profit of $30 billion last year.


The Bank for International Settlements, the central bank to the world’s banks, estimates Australia’s big four are the most profitable banks in the developed world.


In good news for business, the Reserve said the margin on business lending had fallen to where it was before the start of the global financial crisis in 2008.