Unarranged overdraft interest: how the cost builds
An unarranged overdraft occurs when your current account goes below zero without an agreed limit, or beyond an agreed overdraft. UK rules prevent banks from charging a higher interest rate for an unarranged overdraft than the relevant arranged overdraft rate.
Check your account’s annual overdraft rate and how many days you were overdrawn. Since the FCA’s 2020 reforms, personal current-account overdraft charges generally have to be expressed as an annual interest rate rather than old-style daily or monthly borrowing fees, and an unarranged rate cannot exceed the relevant arranged rate.
The interest is driven by balance and time
If your account is £300 overdrawn for two days, that is very different from being £300 overdrawn for a month. Banks calculate interest from the debit balance under their terms, often on a daily basis, even though the price is shown as an annual rate.
A rough simple-interest illustration at 39.9% a year is £300 × 39.9% × 2/365, or about £0.66. The bank's exact result can differ because balances change during the day and compounding rules vary, but the example shows why short, small overdrafts can cost pence while persistent use becomes expensive.
Start with a real-world test rather than the label on the screen. Picture a current account that is £350 overdrawn for seven days. For 'The interest is driven by balance and time', write down the overdrawn balance by day, annual interest rate, any interest-free buffer and incoming-payment dates before changing anything. FCA rules require overdraft charges on covered personal current accounts to be expressed as annual interest, and an unarranged overdraft interest rate must not exceed the relevant arranged-overdraft rate for that customer or comparable account. At a hypothetical 39.9% annual rate, £350 overdrawn for seven days is roughly £2.68 of simple interest before compounding or account-specific rounding, so the duration matters as much as the balance
Unarranged no longer means a punitive higher rate
FCA rules introduced in 2020 stop firms charging a higher rate for unarranged overdrafts than the arranged overdraft rate relevant to that customer/account. They also banned most fixed fees triggered simply by using an overdraft.
That does not mean an unarranged overdraft is harmless. The bank can still refuse payments, and a high annual rate applied repeatedly can become costly. The practical advantage of an arranged facility is predictability and an agreed limit, not a special permission to ignore the balance.
Treat 'Unarranged no longer means a punitive higher rate' as a sequence of checks. Using a current account that is £350 overdrawn for seven days, separate what is confirmed from what is only assumed, then compare the expected result with the actual result. Keep the overdrawn balance by day, annual interest rate, any interest-free buffer and incoming-payment dates. At a hypothetical 39.9% annual rate, £350 overdrawn for seven days is roughly £2.68 of simple interest before compounding or account-specific rounding, so the duration matters as much as the balance If the evidence does not line up, pause before you create another payment, application or instruction because a second action can make the original problem harder to trace.
A payment can be declined instead of creating an overdraft
If there is not enough available money and no arranged limit, the bank may reject a Direct Debit or card transaction rather than let the account go further overdrawn. That can create consequences outside the bank, such as a missed bill or merchant fee.
Turn on low-balance alerts if your provider offers them. A notification at £50 above zero gives you time to transfer money before a £90 Direct Debit pushes the account negative.
A useful decision rule for 'A payment can be declined instead of creating an overdraft' is to take one controlled action at a time. Do not judge the cost from APR alone when you can calculate the pounds for the actual balance and days. In the example of a current account that is £350 overdrawn for seven days, the next step should preserve the overdrawn balance by day, annual interest rate, any interest-free buffer and incoming-payment dates and leave you able to reverse course if new information appears. Ask the bank about support or a cheaper arranged facility before repeated shortfalls become routine.
Use pounds, not just APR, to judge the problem
An annual rate around 40% looks dramatic, but the cash cost depends on amount and duration. Conversely, a £1,500 overdraft used every day can be expensive even if each day's interest feels small.
Review the last three months and add the actual overdraft interest. If you are regularly overdrawn before payday, compare the cost of reducing the limit gradually, moving bills, or using a cheaper structured borrowing option rather than treating the overdraft as permanent income.
Build the fallback before the deadline becomes urgent. For 'Use pounds, not just APR, to judge the problem', decide what you will do if the normal route fails: which official channel you will contact, which reference you will quote and what money or account access must remain available. At a hypothetical 39.9% annual rate, £350 overdrawn for seven days is roughly £2.68 of simple interest before compounding or account-specific rounding, so the duration matters as much as the balance Keep the overdrawn balance by day, annual interest rate, any interest-free buffer and incoming-payment dates together in one dated note so support can see the sequence without asking you to reconstruct it from memory.
Ask for support before the overdraft becomes chronic
If you are relying on an overdraft for essentials every month, tell the bank you are in financial difficulty. FCA rules allow firms to waive or reduce charges in appropriate forbearance circumstances and banks have wider obligations to support customers in difficulty.
Do not take a high-cost loan simply to make the current account look positive for a few days. The objective is to reduce total borrowing cost and stabilise cash flow, not move the same deficit to a more expensive product.
Do not treat documentation as paperwork that comes after the problem. Under 'Ask for support before the overdraft becomes chronic', the overdrawn balance by day, annual interest rate, any interest-free buffer and incoming-payment dates are part of the solution because they show the bank what happened and when. Do not judge the cost from APR alone when you can calculate the pounds for the actual balance and days. Ask the bank about support or a cheaper arranged facility before repeated shortfalls become routine rather than improvising with an unverified workaround.
Sources and verification
James Whitmore - Head of Research
Unarranged overdraft interest is no longer a separate penalty-rate world, but repeated use can still be expensive. Measure the real monthly pounds you are paying and treat persistent overdraft use as a budgeting/borrowing problem early.
MyBankAnswers uses official provider and UK regulatory sources wherever practical. Information is general and does not constitute financial advice.