A while ago, I wrote an article called "How to Owe $40,000 by Doing Nothing," where I pointed out that some companies issuing credit cards charge eye-popping amounts of interest. "As of October 2004," I wrote, "these were the top penalty rates for some major card issuers, at least one of which has probably issued that card in your wallet: . MBNA (NYSE:KRB), 24.99%; JPMorgan Chase (NYSE:JPM), 26.74%; Morgan Stanley's (NYSE:MWD) Discover, 24.99%; Capital One (NYSE:COF), 25.9%; and American Express (NYSE:AXP), 26.74%." Some well-known banks were charging close to 30%!

I recently learned, though, of a credit card interest rate that makes those seem like terrific deals. Apparently, some of our Foolish counterparts across the Atlantic may be socked with nearly 70% interest, if they're not careful! As Creditcardsmagazine.com reported, "Vanquis Bank has launched a card charging a staggering 70% interest rate to the less well-off and those with credit problems. The bank has a range of different choices for customers, starting with its Classic £150 card. This has a spending limit of £150 and an annual percentage rate (APR) of 69.5%."

The story continues: "The credit card has a minimum repayment of 5% each month. Someone who borrowed £150 and only paid the minimum -- initially £7.50 a month -- would take 13 years to repay the debt fully. . On the small debt of £150 plus the £19 annual fee, you'd pay £99 interest in the first year alone, even if you never used the card again and were paying off the minimum each month."

This may be an extreme example, but it should serve to remind us just how powerful and important a card's interest rate can be. It also shows us how easy it can be to end up in financial dire straits. If you owe $5,000 on a card and the interest rate is 70%, that debt, if not paid off, could approach $1 million in a mere decade -- simply from compounded interest. Yikes!

Be smart about your credit card usage. Protect yourself from being taken advantage of by being an informed and savvy consumer. The following articles can help you:

If you or anyone you care about is struggling with credit card debt, head to our Credit Center, which features tips on getting out of debt, along with guidance on how to manage your credit effectively. Really. I mean it. There's some great stuff in there, and it's all free reading. (We even offer a spiffy Motley Fool credit card.)

You can also read about all things credit-related on our Consumer Credit / Credit Cards discussion board.

JPMorgan Chase is a Motley Fool Income Investor recommendation.

The Motley Fool has kicked off its ninth annual Foolanthropy campaign! Nominate your favorite charities on our Foolanthropy discussion board through Nov. 1. For guidelines on what makes a charity Foolish, visit www.foolanthropy.com .

Longtime Fool contributor Selena Maranjian does not own shares of any companies mentioned in this article.