£85.5bn is held in instant-access cash ISAs opened before 2020, with savers earning an average interest rate of just 1.94%, according to analysis from Skipton Building Society.

The analysis of CACI Current Savings Database stock data for June 2026 found that the £85.5bn held across adult instant-access ISAs opened between 2000 and 2019 could generate almost £1.7bn more interest a year if it were earning 3.90%, equivalent to Skipton’s highest-paying easy-access ISA rate at the time of the analysis.

The £1.7bn estimate assumes the £85.5bn balance earning 1.94% was instead earning 3.90%, the rate on Skipton’s two access ISA saver at the time of the analysis.

Skipton said the figures showed the importance of regularly reviewing savings accounts, particularly as many newer cash ISA products offer rates close to twice those being paid on some older accounts.

Alex Sitaras, head of savings at Skipton Building Society, said: “If you’ve had an ISA for several years, make sure you check the rate and compare what you’re earning with what’s available on the market, as many savers don’t realise their interest rate is no longer competitive.”

Skipton’s survey of 2,000 UK adults also found that 29% think about their personal finances daily, although the building society said savers may be overlooking the opportunity to improve returns by reviewing existing accounts.

Rachel Springall, Finance Expert at Moneyfacts, said: "The scale of cash earning such poor rates within an ISA wrapper is a stark reminder of how much savers could be missing out on by assuming their interest rate is still competitive.

"It’s easy for savings to be overlooked, particularly when an account has been held for several years and savers are familiar with their provider or simply don’t think to review the rate. A regular review of savings accounts is well worth the time, particularly for those who are looking to make their money work harder amid ongoing household cost pressures."

Springall added that savers should use a provider’s formal ISA transfer process rather than withdrawing and reinvesting the money if they want to retain the tax benefits of the ISA wrapper.

---