Back to school shopping can take a big bite out of your budget, so when stores offer a deep discount for opening a new credit card, it may be hard to resist. The experts at Consumer Reports did their homework and say in many ways, these cards fail to make the grade.

After analyzing the data, Consumer Reports says store credit cards rarely rise to the top of the class. For one thing, the interest rate is often much higher. On average they range at about 24 per cent, well above other bank credit cards that are around 15 per cent.

Applying for any new card can also temporarily lower your credit score.

“Every time an inquiry is made on your credit card account it hurts it a little bit and while it may not seem like that much it could be the difference between a good credit score and a bad credit score,” said Nikhil Hutheesing, Consumer Reports money editor.

If you do open an account, don’t shut it down immediately because that has a negative impact on your credit score as well. The best thing to do is put the card away and don’t use it.

If you are looking to build your credit, store cards, which can be easier to get approved, could be a good way to get your foot in the door. And if you shop at the store often, having the card could unlock special discounts or earn points.

But remember, with the high interest rate, it’s especially important to pay your bill in in full.

“If you don’t it’s going to undermine the whole purpose of getting the card in the first place,” explained Hutheesing.

And make sure you always pay that store credit card on time. If you only use it once or twice a year, it can be very easy to forget the due date.