RBS has said it could cost up to £175 million for it to redress the effects of an IT failure that hit balance updates at RBS, NatWest and Ulster Bank this summer.
The £175 million charge, detailed in RBS' Q3 results, has been set aside to include compensation for the incident.
RBS has revised the figure up by £50 million from a Q2 estimate due to the length of time Ulster Bank customers suffered problems, RBS said on Friday.
In June a maintenance error traced to one of the banking group's Edinburgh data centres caused a batch-processing glitch.
Customer balances could not be updated, creating a backlog of work at the banking group. The huge backlog itself then added to the confusion.