The interest rate (the cost of borrowing money): Borrow 1.000 at an APR of 20% over one year and you will be charged £200 interest (20% of 1.000 £) calculated. So the lower the interest rate, the less debt will cost you.
The length of the loan: this is just as important as the interest rate. The longer you borrow, the more interest you will be charged, as 20% APR means you will be charged 20% of your outstanding debt each year plus interest on previous interest. This is critical with minimum repayments, as by repaying the minimum amount you are effectively borrowing longer and therefore paying much more interest. So the faster you pay back, the less it will cost you.
Minimum repayment: Unlike mortgages and loans, with credit cards you choose what you pay back; the more you pay, the faster the debt disappears. The only caveat is that there is always a mandatory minimum repayment: the lowest amount you must repay each month to avoid a fine. Instead of a fixed amount, it is typically 2% or 3% of outstanding debt, with a minimum of £5. We need to pay down debt as quickly as possible, but credit card companies want us to pay down debt and earn them interest. Minimum repayments should do just that.
It's important to understand that the minimum is a percentage of your outstanding debt, and as your debt goes down, the amount you pay back also goes down. This means that most of your repayment is usually just used to pay that month's interest, rather than actually reducing the amount you owe. There are two main reasons why most people only make the minimum repayments. The first is because they just don't know how damaging it is; if you are, just increase the amount you pay back immediately and the problem is solved.
But for most, it's because they simply can't afford to pay more than the minimum. If this is you, please consult a financial advisor or someone who can help you manage your debt.
What you can do: simply make a fixed repayment based on what you can afford; rather than allowing the repayment to drop each month. Always set up a direct debit to repay credit cards automatically, as this means you will never be fined for missed or late payments.