On average credit card holders have incurred £267 in charges when the interest-free period has ended, a total of £623m across the UK.
Nearly a third (31 per cent) said they received no notice from their provider that the interest rate was increasing.
As a result, 82 per cent of credit card holders took an average of four months longer to pay back their balance. Some 85 per cent would consider switching to a better rate if they had been warned their deal was due to expire.
Credit card providers entice customers with attractive introductory zero per cent offers that can now stretch up to as much as 40 months. But the longer the deals, the greater the risk that consumers forget when they took out the credit card in the first place, with serious implications. When the introductory offer is over, the interest rate jumps to the provider’s standard APR which can be up to a staggering 34.9 per cent.
Tashema Jackson, money expert at uSwitch.com, says: "Credit card providers are wooing consumers with tempting zero per cent deals but when the rates rocket without warning, the honeymoon period is definitely over. We are calling on providers to give customers clearer and more prominent notice before jacking up the interest rate, to help people better manage their debt."
Jackson advises credit card holders to keep a record of non-chargeable rate in order to prevent an extra charge to their monthly payments: "In the meantime, the onus is on credit card holders to plan ahead. Put a note in your calendar when you take out a card for a couple of months before the perk is due to end. This will give you time to research other deals on the market and transfer your balance."
The Card Association states that there is £61.1bn owed on credit cards across the UK, of which 43 per cent is interest free or paid in full without accruing any interest.