Consumers could be leaving over £1 billion to sit idle in "zombie" current accounts, a survey has found.
More than one in three (37%) people have two or more accounts, but nearly half (49%) said they only use one of them on a day-to-day basis, comparethemarket.com found.
The average amount people said was sitting in an unused account was £141, which could equate to more than £1 billion sitting in unused accounts if the findings were projected across the UK, the website calculated.
Nearly one third (31%) of those with more than one current account had originally opened another account to get a particular reward on offer.
But one in eight (12%) people with multiple accounts said they checked their unused account as little as twice a year.
Many people seemed unsure whether their money could be working harder elsewhere.
Over half (56%) did not know whether their bank had cut interest rates in the past year and 58% did not know the interest rate on their current account.
Several current account providers have announced rate cuts in recent months, following the fall in the Bank of England base rate to 0.25%.
Jody Coughlan, head of money at comparethemarket.com, said: "It is concerning to see how many people have over £100 sitting in these unused zombie accounts.
"Whilst it is a good idea to have a 'rainy day fund' set aside in case of emergencies, the fact that so many people don't regularly check their additional accounts is a risky move to take.
"It is really important to regularly check your personal finances for unusual activity and prevent financial losses.
"Unused accounts are easy targets for hackers who might be able to steal hundreds of pounds without it being detected.
"Similarly, recurring direct debits from forgotten accounts can cause customers to unknowingly go into their overdraft and incur hefty fines."
More than 2,000 people took part in the research.