A bank has pledged to make it clear to customers if they have money sitting in their current account that is not earning credit interest.
Tesco Bank said that the monthly statements of its current account customers will show "foregone interest" - the amount of interest that they could have earned if they had transferred their current account balance in to an instant access savings account with the bank.
Tesco is a relatively new player in the current accounts market, having launched its first current account in June 2014 with a promise to shake up the sector.
Its current account pays 3% on balances up to £3,000, and charges a £5 fee unless holders pay in £750 a month.
The move will mean that people with more than £3,000 sitting in their account will be able to see how much cash they could have earned by moving their remaining money into an instant access savings account with Tesco, which currently pays 0.6% interest.
The comparison will not look at what customers could receive if they moved to another bank, although it may encourage more people to think about where they are holding their money.
Many current accounts pay no interest at all in the low interest rate environment, and while they may appear to be "free", people pay in other ways, for example through overdraft fees or foregoing interest which they could have received from an account elsewhere.
A new seven-day current account switching service was set up across the industry in 2013, aiming to make the process of ditching your old bank and moving to a new one easier.
Tesco's head of current accounts David Millington wrote on a blog on the bank's website: "The banks' biggest source of current account income isn't fees or charges. It's actually the money they generate by lending out the salaries and other income current account customers pay into their accounts. This is called foregone interest.
"And because 80% of current accounts don't pay any of that income back to their current account customers, the banks are able to generate a combined total of £3.2 billion every year from foregone interest alone - nearly £50 per customer. That's a lot of money that many customers don't know their banks are making at their expense."
Rachel Springall, a spokeswoman for financial information website Moneyfacts, said: "More consumers need to be encouraged to check whether their current deal is best for them and if they are not happy they should vote with their feet and use the seven-day switcher service to get something better.
"Transparency on bank accounts is a key issue and has been debated more frequently than ever before, so any efforts to make it easier for customers will be welcomed in open arms, especially if it helps them boost their savings or save on fees.
"Including any other savings deals within a statement is handy for consumers who want to spread their wealth, but as always it's beneficial for savers to keep on top of best buy tables and watch out for any bonus rates."