Well, as they say, looking doesn't cost you anything. Simply browsing online credit card offers won't hurt your credit score one bit, if you're just window shopping and deciding what's most important to you - the biggest rewards or the lowest interest rate.
But actually filling out an application and turning it in? Yes, absolutely, that can affect your credit score.
Here's why: When you apply for a credit card, you're applying for a line of credit. Too many new lines of credit can bring down your credit score and negatively affect your ability to get additional credit. In other words, the more cards you apply for in a short period of time, the less likely you are to be approved.
I know that's frustrating, because it would be nice if getting a credit card was a little like applying for college or a job. You'd apply to, say, 10 cards and see who says yes and no, and then out of the eight that say yes, you choose the one or two that you want.
That would be great, but a lender has no way of knowing that's what you're up to. If they see you've applied for 10 credit cards, or even, say, three, they're going to assume that you probably have some major financial problem, and you're trying to raise money and keep your life humming along by signing up for as many credit cards as you can. And they're going to assume that these problems may prevent you from paying back whatever you borrow on your cards. And not only will you probably be rejected, applying for a slew of cards all at once will likely set your credit score back a bit.
So applying for a credit card isn't something you should do lightly. You're really announcing your intention to draw on the new line of credit. If you do obtain a new card and then decide you don't want it, you can, of course, simply cut it up and have the credit card company cancel your account. Because if you have, say, a $3,000 line of credit open that you're not using and never intend to use, a lender won't know that, and that could prevent you in the future from getting a credit card that you really do want.