Three of the country's big banks quietly cut interest rates for online savings accounts last month, as lenders try to limit a crunch on their profit margins being caused by stiff competition and soft economic conditions.

National Australia Bank, ANZ Bank and Westpac all reduced rates for popular online savings accounts in November, the same month in which customers also started paying higher mortgage rates.

Pressure on banks' profit margins is prompting them to cut online deposit account interest rates.

ANZ Bank cut the base rate on its online saver account by 0.2 percentage points to 1.8 per cent, while NAB reduced its iSaver base rate by 0.1 percentage point, also to 1.8 per cent, interest rate comparison website Mozo said.

As well as cutting base rates – the long-term rates paid to customers outside "bonus" or limited-time promotional offers – lenders also cut their limited-time "introductory" rates used to lure new customers.