Even though credit cards offer convenience, they often can be a trap, leaving you with mountains of expensive debt. Rather than thinking of your credit cards as a way to spend, you can turn them into money-earning devices.

As long as you make your payments faithfully, the judicious use of credit cards can be quite profitable.

1. Get Money With Discount and Cash-Back Credit Cards

To make money using credit cards, get cards that pay you to shop. These types of cards are called cash-back credit cards.

Capital One’s Quicksilver card gives you 1.5 percent cash back on every purchase you make. If you tend to shop in one store more than others, consider a store card. The Kohl’s credit card, for example, gives you between 15 and 30 percent off on most purchases you make at the store, even online.

The more you use a cash-back or store credit card, the more cash or discounts you can earn. Be careful, though. Pay off your credit card balance in full every month to avoid racking up credit card debt and paying high-interest charges. If you fall too deep into debt, the rewards might not be worth it.

2. Invest Your Cash Back

You can also put cash-back rewards to work for you and invest the money — even if you earn less than a few hundred dollars. Thanks to the power of compounding interest, your cash-back rewards can grow into a sizable nest egg over time.

Let’s say you earn $300 in cash back every year. If you invest that $300 into an account that earns 7 percent interest annually, then in 10 years your balance will grow to more than $4,000.

As an added credit card benefit, some rewards credit cards allow card owners to link their cards to eligible investment accounts. Take the Fidelity Rewards Visa Signature credit card: You can earn unlimited 2 percent cash and have those rewards automatically deposited into an eligible Fidelity account, such as a brokerage account, a 529 college savings plan, a retirement account or another account.

To maximize your investment earnings, look for credit cards with no restrictive categories. The more restrictions the card has, the fewer opportunities you have to cash in and invest your rewards.

3. Do Your Shopping Online

As a credit card benefit, some cards allow you to earn cash back or points just by shopping online. You might need to log into your credit card account in order to access these savings and take advantage of the deals. For example, eligible Discover card members can earn additional cash back when they shop through Discover Deals. This includes 5 percent cash back when they shop LivingSocial, Apple, Walmart and other online retailers.

As a cardholder, you can also score gift cards or savings off your next purchases. Other credit card issuers have similar shopping portals, but whichever shopping portal you use, read the terms and conditions fully in order to understand how the program works.

4. Earn Free Cash Using Your 0% Cards

Many cards offer a 0% interest rate for a certain time period, such as one year. To earn money on that type of card, place your daily charges on the card and only pay off the minimum balance. Place the amount you charge into an interest-bearing account, such as a money market fund. Although you won’t get rich even with the best 0 percent purchase credit cards, you’ll be able to earn income on that money as your credit card balance accrues no interest charges.

When the promotional 0 percent time period expires, transfer the money from your money market fund to pay off the balance, and keep the interest you’ve earned. You can also get cash this way from balance transfer credit cards, but be aware that balance transfer cards typically charge a fee of 3 percent or more.

By the way you can also use the newest feature of Money Lover: Credit Wallet to start managing your credit card in a more effective way.