Most of us are trying to limit the amount of plastic in our lives. Yet there’s one plastic we just can’t seem to ditch: our credit cards.

Oh the shiny, pretty plastic. The weight of it in your palm. Credit cards make online shopping convenient and splitting the restaurant bill simple. What’s not to love?

Credit cards may seem like your friend, but be warned. Credit card companies have sneaky ways to get your money. Otherwise, why would they make them?

How Credit Card Interest Works

Credit card debt sucks because credit card interest sucks. Credit cards have extremely high APRs.

APR: Annual Percentage Rate. How much interest a bank will charge on bills not paid in full

The interest on a card will either be compounded monthly or daily. By compounded, we mean calculated, or added up. Credit cards with more rewards and perks tend to have higher APRs. They typically range from 15-25%.

Like any new relationship, credit cards like to start off strong with a new customer. They offer sweet sign-up perks like waived fees, free airline miles and 0% introductory APR for a set period. Those could be as long as 18 months.

That’s how they get ya.

Banks issuing credit cards make money on interest payments and late fees. They prefer customers who don’t pay their full card balances every month. So, like any new relationship, ask some questions. Will I like this card six months from now? Can I afford the $150 annual fee after the free year ends? Can I get over the fact it leaves crumbs everywhere, like a human Nature Valley granola bar? (Ok, the last one isn’t about credit cards.)

Short-term relationships, fine. But short-term credit cards, not so great. Open and close cards too often, and it could damage your credit score.

I’m in a new relationship…with my credit card

Fiona signs up for a platinum gold phosphorescent lightning green credit card with Dunkin’ Donuts and AMC Movie Theater rewards points. #thebestcombo #wherecanigetone

Her fancy new card has a sign-up offer of 0% APR for 12 months. The first couple months, she forgot to set up automatic bill payments, but she doesn’t worry because #0%. Six months in, she’s charged $5,000 to the card. Ok, she thinks, I just need to pay back that money before my 0% ends.

She starts to make regular monthly payments, while still using the card. By the end of her 12 months, she has an outstanding balance of $4,500. Too much Dunkin’.

Now that the 0% days are over, her card has a 20% APR. Using a handy credit card payment calculator, Fiona calculates with $200 monthly payments, it will take her over two years to pay it all back. Plus, she’ll pay $1,157 in interest. That’s a year’s worth of Dunkin’ lattes (with almond milk!).

The truth about credit card debt is that it builds quickly. Especially with credit cards that offer a 0% APR for the first months or year of owning the card, it’s hard to fork up a year’s worth of credit card charges once the 0% APR ends. Main takeaway: Spend what you can afford. Pay the full credit card balance in full each month. Even with #0%.

RECAP

Credit cards are fun and convenient. But they can cause serious debt if you don’t pay your balance in full every month.

APR: Annual Percentage Rate: The interest rate the banks charge you if you don’t pay back all the money you charged that month. National average is around 16%.

Remember, if you can’t pay your full bill, pay at least the minimum payment (or more), rather than pay nothing. Late fees are no good either.