Both new and existing Nationwide customers could see themselves more than £650 better off, on average, according to emails recently sent to members.

The world's largest building society has announced its latest ISA rates, telling customers: "Open a cash ISA now and get up to 4.25%. And because you're saving tax free, you keep every penny of interest you earn."

Anyone who transfers their funds into these accounts would receive the additional cash, providing they adhere to specific criteria.

Currently, Nationwide is providing four fixed rate cash ISAs, offering rates of up to 4.25%. A 2025 survey by Finder showed the average savings held by UK residents currently stands at £16,067.

Should this sum be deposited into a one year fixed rate cash ISA with Nationwide, which carries a 4.05% interest rate, savers would be £650.71 better off after the twelve months is up.

The five year fixed rate cash ISA boasts a 4.25% interest rate, meaning typical savers would be a substantial £3,717.05 better off when the term expires - though this requires committing your funds for a full five years.

Applicants must be a UK resident, Crown employee serving overseas, or partner of a Crown employee, Nationwide said.

You must also be aged 18 or over, and you can't have used up your annual ISA allowance - this tax year, you can pay in up to £20,000 across your ISAs with any provider.

Should you need to withdraw funds before the fixed term concludes, the account will be closed and an early access charge will be payable.