TSB has reported it suffered a statutory pre-tax loss of £105.4 million in 2018, blaming the impact of its IT meltdown.
The bank said the disastrous migration of its IT system resulted in £330.2 million of foregone income.
It also blamed costs due to customer compensation, additional resources and fraud.
Around 80,000 customers switched their bank account away from TSB in 2018 – 30,000 more than 2017.
The bank said it had recovered £153 million from IT provider Sabis.
TSB executive chairman Richard Meddings said: “Last year was TSB’s most challenging year. But we enter 2019 with renewed ambition to re-emerge as the leading challenger bank in the UK – firmly on the side of the customer.
“We have a truly customer-focused team, a strong banking system that customers are starting to see the benefits of, and look forward to our new CEO, Debbie Crosbie, joining us later this year.”
Up to 1.9 million digital and mobile banking customers were left unable to access their accounts in April last year after work to transfer its IT system failed.
The tech troubles were triggered by a migration of customer data from former owner Lloyds’ IT system to a new one managed by the bank’s Spanish owner, Sabadell.
Chief executive Paul Pester stepped down in the wake of the fiasco.
The bank announced his replacement, former CYBG chief operating officer Ms Crosbie in November.
TSB said she will join the business in the spring.