One of the main ways credit cards try to reel in new customers is by offering a sign-up bonus. After spending a certain amount within the first three months of account opening, you'll earn cash back, rewards points or travel miles in quantities that far outstrip the card's standard rewards-earning rate.

These sign-up bonuses can be the icing on the cake for an already sweet deal, or they can be a trap that locks you into high maintenance fees and interest rates while offering you little in return. Here are a few questions you should ask yourself before you consider applying for that new credit card just to get the sign-up bonus.

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How much do you need to spend and in what time frame?

Most cards usually require you to meet the sign-up bonus requirements within the first three months after opening the account. Whether or not this is doable depends on how much you need to spend in order to get the bonus. A typical cash-back rewards card may only require you to spend $500 in a three-month period while some of the top travel rewards cards may require you to spend several thousand dollars during the same time frame.

Look at how much you usually charge to your credit card in three months to determine how likely you are to actually meet the sign-up bonus requirements. If it would require a big increase in spending, you may not get the bonus. Or worse, you may end up spiraling into credit card debt as you charge more to your card than you can afford to pay back at the end of the month.

If you don't feel confident that you can easily achieve the sign-up bonus without dramatically altering your spending habits, it may not be worth pursuing. That doesn't mean you shouldn't sign up for the card, but you should judge it by its ongoing rewards rather than its sign-up bonus.

How much does it cost to own the card?

Some credit cards charge annual fees, which can counteract the value of the card's rewards. Annual fees are most common among high-end travel rewards cards, but some cash-back rewards cards charge them as well.

Before you sign up for the card, check to see whether it charges an annual fee or any monthly maintenance fees. Some cards waive these fees for the first year, only to begin charging them as soon as you hit Month 13, so don't be fooled by marketing language that promises a $0 annual fee. Always check the cardholder agreement for the full details.

Unfortunately, annual fees don't count toward the sign-up bonus requirements, so you may end up paying even more than you thought in order to get the bonus. Don't forget to calculate the cost of these fees when determining how much you can realistically afford to spend in three months.

How do the card's ongoing rewards stack up?

Chances are, you're not going to cancel the credit card as soon as you hit the sign-up bonus. That means it's important to pay attention to the ongoing rewards-earning rate as well. Some cards offer a standard rewards rate on all purchases while others have rotating categories that give you special deals on select items throughout the year.

Look at the ongoing rewards schedule and estimate how much you'll earn in rewards each year. Then, compare that to the card's annual fee (if it has one). In order for it to be worth it, you should be earning more in rewards each year than you're paying to own the credit card.

How's your credit score?

Every time you apply for a new credit card, the card issuer will do a hard pull on your credit report. This will cause your credit score to take a slight hit. A single hard inquiry here and there won't damage your credit significantly, but if you're applying for half a dozen new credit cards every year, it's not uncommon to see your score drop as much as 30 points before gradually recovering. This can hurt your chances of being approved for new credit cards or loans in the future.

Think carefully about how likely you are to get approved for the credit card before you apply. If your credit score is 500, you won't qualify for the top rewards cards, so all applying is going to do is drop your credit score a little further.

A credit card sign-up bonus can be a nice perk, but it's important to be realistic about what you can achieve. You also need to take other features into account, like the ongoing rewards-earning potential and any fees associated with the card. After all, you can only earn the sign-up bonus once, but the rest of it will stick with you for as long as you own the credit card.