If used responsibly and properly, credit cards are wonderful tools. Prudent use can help you establish such a stellar reputation, you’ll have no trouble obtaining the significant credit required to buy a home, finance a business, get a degree, and all sorts of other wonderful lifestyle options for which borrowing is likely the only option. They can help you over occasional hurdles and take the pressure off during emergencies. Without a credit card, you’ll have trouble reserving a hotel room or an airline ticket. They can take the stress out of your holiday shopping by allowing you to do all your buying online from the comfort of your couch. Many credit cards come with benefits, like points accruals that help you get membership awards or cash back, or they come with travel insurance or provide extended warranties or other perks. They also protect you from the vulnerability of carrying cash.

As positive and useful as they can be, though, they can be equally negative and destructive if they aren’t used properly.

Credit card interest is compounded, which means that if you fail to pay your balance off each month in full, the following month you’ll pay interest on the interest; for example, if you pay off a balance of $10,000 at 17.99% APR (annual percentage rate) by making only a minimum payment of 3% of the balance each month, it would take you more than 17 years and cost $9,487 in interest — that’s almost as much as the principal! (Your minimum payment will typically be anywhere from 1% to 4% of your balance.) To really appreciate the effect of credit card interest, before you charge something you can’t pay off immediately, ask yourself how much more you’d be willing to pay.

for it. A $90 movie night doesn’t seem like such a deal when you realize it’s actually going to cost you $180 by the time you pay for it.

In some cases, banks will let you make interest-only payments on a line of credit, which means you could conceivably carry the debt for years and never even touch the principal! Obviously, this arrangement is beneficial only to the lender.

Make sure you always read the fine print. Sometimes, a reasonable interest rate will jump considerably if you are late on even one payment. Another way lenders attract users to their credit card is to offer an APR that is low initially, but increases considerably after six months or a year.

Stay away from cash advances; while convenience cheques can be handy for transferring balances from higher-interest cards, be wary of them too. While interest on a credit card purchase usually doesn’t start to accrue until after your payment due date, giving you a chance to pay it in full without accruing any interest at all, cash advances are charged interest from the day you take them, and often at a higher rate. Low introductory rates won’t apply to them either.

Using credit cards to meet basic needs, like paying rent or buying groceries, transferring balances around to keep up with payments, failing to open your credit card statements, consistently making late payments or paying only the minimum, and having credit cards that are maxed out to their limits are all signs that you’re headed for financial trouble. If this sounds like you, call a qualified credit counsellor today.