What a credit card sign-up bonus?

Opening up a new credit card is a great way to build credit, and sometimes you can even be rewarded for doing so.

Many cards offer a welcome bonus, or enhanced cash back, points or miles for a limited time. To earn the bonus, you usually have to reach a minimum spending requirement within the first few months, anywhere from $500 to $5,000.

You likely have seen a card issuer advertise welcome bonuses for their credit cards on their website or on mail offers you receive at home. They include language promising "bonus points" or a certain dollar amount of cash back when you sign up and spend on a certain credit card. These sign-up offers, also referred to as welcome bonuses, encourage you to open a credit card account and start using your card right away.

The best credit cards offer alluring bonuses that can add hundreds back to your wallet, but you usually have to first spend money on your card in order to earn the bonus. On the bright side, this actually makes the bonus rewards you receive non-taxable income when it comes to doing your taxes since you had to earn them by spending money. Bonuses are considered a rebate, not a form of income.

In addition to requiring a minimum spend, welcome bonuses come with time requirement as well. Most cards require that you spend anywhere from $500 to $5,000, and it usually must be charged onto your card within the first three months (or 90 days) of your account opening.

After meeting the minimum spending requirement to earn your welcome bonus, how quickly the points or miles post to your account depends on the card issuer.

For example, with the Capital One Savor Cash Rewards Credit Card that lets new cardholders earn a one-time $200 cash bonus once you spend $500 on purchases within the first 3 months from account opening.

With a travel rewards card, such as the Chase Sapphire Reserve® (see rates and fees) that offers 150,000 bonus points after you spend $6,000 on purchases in the first 3 months from account opening.

If you are planning on using your welcome bonus to buy a specific purchase or plan a trip somewhere, be sure to take these time requirements into account.

Charging hundreds or thousands of dollars onto your credit card within a short period of time seems like an expensive way to earn rewards, but if you have a large purchase to make or an upcoming vacation to plan, a welcome bonus can actually come in handy.

For instance, one financial expert we spoke to met the minimum spend on her new credit cards by charging her and her husband's wedding rings and the cost of a small wedding. The couple then used the cash back she earned from welcome bonuses to help offset the cost of their honeymoon. Of course, you should take processing fees into consideration (some businesses charge 2% to 4% for credit card transactions), but if there are no extra fees this method can be quite helpful when financing large purchases like trips.

And once you do use your credit card to earn a welcome bonus, it's essential that you pay off any large balances quickly so you don't accrue interest that offsets the value.

Here's some math to show how quickly interest adds up:

If you were to meet the minimum spending requirement of $6,000 within the first three months from account opening on the Chase Sapphire Reserve®, you can earn 150,000 bonus points.

However, this value is almost negated entirely if you let that $6,000 balance sit unpaid for a year. The regular variable APR on this card ranges from 19.49% - 27.99%, and even with an interest rate on the lowest end at 19.49%, you would accrue hundreds of dollars in interest on a $6,000 balance over 12 months. Because of the high interest credit cards charge, make sure you can pay off whatever you spend to earn the bonus.

Here are some of the top cards of Select's round-up of the best credit card welcome bonuses.

• Winner: TD Cash Credit Card
• Best for travel: Chase Sapphire Reserve®
• Best for cash back: Capital One Savor Cash Rewards Credit Card
• Best for no annual fee: Capital One Quicksilver Cash Rewards Credit Card
• Best for no spending required: Prime Visa (See rates & fees)

If you're interested in earning more rewards with a new credit card, consider one of the above that can help you make some extra cash when you spend.

Information about the TD Cash Credit Card has been collected independently by Select and has not been reviewed or provided by the issuer of the card prior to publication.

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