Nationwide says a free online tool has identified £115 million in additional annual financial support for households since it launched last year.
The Better Off Indicator helps people discover benefits and other financial support they may be entitled to but are not currently claiming.
The tool has identified an average of £555 a month in potential additional income for eligible households.
Developed in partnership with Policy in Practice, the service is available to Nationwide customers, Virgin Money customers and the wider public.
It can be accessed online, through the Nationwide mobile app, by phone or in branch.
More than 17,000 households have identified potential entitlement to additional annual support since the tool launched.
Nationwide also said more than 550,000 customers have accessed information about financial assistance through its website and app.
The service has been designed to make accessing support easier for people who may lack confidence online, are digitally excluded or prefer face-to-face assistance.
The expansion to Virgin Money customers is expected to allow even more households to access the free service.
Nationwide's findings come as households continue to face financial pressure.
Research carried out by Nationwide with Action for Children found that 66% of parents receiving Universal Credit are worried about being able to afford food during the summer holidays.
Many parents also said they expected to rely on borrowing to make ends meet.
The research found that 63% were likely to use Buy Now Pay Later schemes, while 60% anticipated borrowing from friends or family and 59% expected to use credit cards.
More than half of parents said they may delay paying essential bills during the holidays, while half said they were likely to postpone rent or mortgage payments.
Nationwide estimates that around seven million UK households are missing out on financial support, with a lack of awareness, complicated systems and stigma around claiming benefits among the reasons.
