This is a change from a previous buffer of £100 and comes on top of an interest rate of 19.89% already being charged on certain current accounts.
A host of other charges are also being introduced which will leave current account customers out of pocket.
NatWest and RBS current account charges
Customers with an authorised overdraft who go over the limit by more than £10 will be hit with a £6 fee from Friday.
This will apply to those with any of the following accounts: Select account, the only free account on offer from the bank; Select Silver account, which is £10 a month; and the Select Platinum account, priced at £16 a month.
The move from RBS mirrors other overdraft charges from the high street banks, such as Halifax charging between £1 and £3 a day for those dipping into an authorised overdraft and £5 a day if it's unauthorised.
The buffer of £100 will remain for customers with an advantage gold account, which costs £15 a month to open, or a select platinum account, which has a monthly charge of £16.
Any existing current accounts or private bank accounts are also being changed to select accounts, which will face the new fees.
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How to avoid being charged
Dipping into an overdraft can be a handy tool if you're stuck for cash or have to pay a surprise bill. However, it can also be expensive especially if it's an unauthorised overdraft you're relying on.
Careful budgeting is the key way to staying in the black, but another handy tool is setting up an alert service to let you know when you're near your overdraft limit. Most banks have this option and it's free to set up.
Making use of a budgeting tool like Lovemoney's MoneyTrack will help you keep on top of your balances to keep the time you spend in the red to a minimum.
Alternative current accounts
Shopping around and switching current accounts is another way to avoid these new charges. Here are five of the best current accounts with no overdraft charges.
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