But with the big players in the Irish financial services sector earning over €3 billion last year the cost will just be a blip on the profit and loss accounts, analysts said.
Scott Rankin of Davy Stockbrokers estimated Bank of Ireland would lose between €12m and €15m if it implemented a full 0.5% mortgage rate cut for customers.
Since Rankin made those forecasts however AIB has decided not to implement the full cut with borrowers getting a little over 0.3% of the reduction while Bank of Ireland has gone the whole hog with a full 0.5% being passed on to borrowers.
However AIB made no reference to the impact of the cut in mortgage rates to its bottom line when its issued its trading statement for the current year.
While it forecast a drop in its earlier earnings forecast it made no attempt to blame the downturn in its earlier forecasts on the impact of the lower mortgage rates.
It said the cut in earnings growth from mid single digit figures to low single digit figures was due mainly to down to losses in currency translation, particularly from the dollar and sterling areas that have seen their currencies fall by 12% and 6% this year against the euro.
AIB said there were once off factors in the Irish market last year that was also a factor in the revised earnings for the current financial year.
In his analysis Rankin suggested that full cut of 0.50% would cost the two major banks €30 million in total while David Went, boss of Irish Life & Permanent said the loss to his organisation would be in the order of €10 million.
First Active, with about 12% of the Irish market, was set to lose up to €2 million due to the lower margins that would operate after the reductions were introduced.
As things stand Bank of Ireland has cut by the full 0.5% and it remains to be seen what impact if any the reduction will make to the bottom line.