The amount paid back is calculated as a percentage of your total spending. Percentages vary, but typically range from 0.5% to 2%. Some card issuers pay higher rates for purchases in some categories or made through certain retailers. The Discover? Platinum Card, for example, offers up to 1% cashback normally, but 5% on purchases made from selected merchants in their Get More Program.

Cashback is obviously an attractive incentive, but if you are likely to leave a balance outstanding on your credit card, it should not be your first priority when deciding what card to pick. For one thing, many card issuers only offer cashback as long as you clear your balance every month. For another, if you are paying interest, the cost of this will probably far outweigh the benefit of cashback. In such instances, your first priority should be to pick a card with a low APR (annual percentage rate) and/or a long interest-free introductory period.

If you are confident you will be able to pay off your balance every month, cashback is certainly one feature you may want to take into consideration when picking a card. There can be a few surprises lurking in the small-print, however, so before applying for a cash-back credit card it's very important to read this carefully. In particular, you should check the following:

* Is the headline rate paid on all purchases, or only those after a set amount of annual spending? The Discover? Platinum Card, for example, pays just 0.25% on your first $1,500 of spending each year, and 0.50% on the next $1,500. You then earn a full 1% of each purchase made after your total amount of purchases exceeds $3,000.

* Is there a cap on the total amount of cash back you can receive in a year?

* Is the cashback payment made by check, or is it simply a reduction in your bill?

* Is there an introductory bonus offer (e.g. a higher rate of cashback for your first six months)? If so, check how long this lasts, and what happens to the cashback rate afterwards.

* Is there a scheme offering you the opportunity to trade your cashback for bigger discounts with selected merchants? If you are likely to spend money with these merchants anyway, this may have added appeal.

* Are there any hidden costs, e.g. an annual fee or a fee to redeem your cash back credit?

In recent months some card issuers have been cutting back on their cashback offers, reducing the rates paid or in some cases abolishing it altogether. If you want cashback, therefore, it's very important to shop around, and not simply respond to the first offer that drops unsolicited into your mailbox. Credit card comparison websites such as www.finest-credit-cards.com make this easier by displaying all the best current offers, updated daily, alongside unbiased advice on choosing and using a credit card.