Moving ISA savings around to make the most of competitive interest rates could help people make a better return on their capital.
Consumers could make over a grand each year if they put their money into the correct Isa.
ISA savers may be losing up to £1,300 a year in interest payments by failing to move their money into accounts that have more favourable rates.
Many banks do not allow customers to transfer their cash into better accounts and some have been cutting back rates on older ISA plans, which has left many consumers feeling shortchanged.
Michelle Slade of the data provider Moneyfacts.co.uk said: "Many people are sitting on sizeable savings if they have taken out ISAs over the past decade. So while it makes sense to check you're getting the best rate you can on any new Isa, the priority should be to make sure your existing Isa savings are still earning a fair rate".