The nation's depositors have been dealt a fresh blow with the Commonwealth Bank becoming the last of the four major institutions to slash interest rates to virtually nothing on its savings accounts.

Financial data firm Canstar confirmed on Tuesday the CBA had halved the rate on its online savings account, taking it down to 0.15 per cent.

It follows the decision of the Reserve Bank of Australia earlier this month to cut official interest rates by a quarter percentage point on top of their June reduction.

CBA has become the last of the big four banks to cut deposit rates which now sit at an all time low. Credit:Josh Robenstone

Across the four major banks, all have now cut the rates on their online flexible savings accounts by at least 0.39 percentage points since the start of the year. NAB has the lowest at 0.11 per cent on its iSaver account while the CBA, ANZ and Westpac are offering 0.15 per cent.