A friend showed me her credit-card bill last month. Her balance was $425. Her minimum monthly payment this month was listed as “$0.00.” My friend said, “Look at that, I have one month free.”

Free, in a pig’s eye. The interest keeps on accumulating, on any payment you fail to make.

The bank gave her this apparent “free pass” because she had paid substantially more than the minimum the previous month. By paying more than the minimum, you reduce the total amount of future interest you owe.

But if the bank can talk you into skipping a month, the amount of interest you owe runs right back up.

Many banks run skip-a-month promotions during the summer-vacation season, or at Christmas.

“They try to pass this off as a saving to consumers,” says Robert McKinley of CardWeb.com, an expert in credit-card rates and fees. “But you’re being misled.”

If you do choose the minimum payment, you’re typically getting rid of no more than 2 percent of your outstanding balance every month.

Cards with low-interest rates might ask you to pay only 1.5 percent of what you owe. The less you pay, the more interest the bank will earn.

Some consumers foolishly stick with the minimum, even though they could pay more, says Steve Rhode, president of Myvesta.org, an online debt counseling service.

He cites the response of one woman, whom he had advised to raise her monthly payments. Said she, “I’m not giving them (the banks) another penny more than they’re owed.”

Ironically, by refusing to prepay, she could lose almost double the amount of her original loan in interest costs.

I asked Rhode to calculate how long it would take to repay a $5,000 debt, at 16 percent interest, if you paid 2 percent each month.

The amazing answer: more than 35 years. That’s 35 years to pay for a Twinkie, if you put your groceries on a credit card.

Here’s why it takes so long. When you pay 2 percent of a declining debt, your payments get smaller and smaller each month. So your debt will last longer than you think.

Over 35 years, you’ll pay $9,329 in interest, on a $5,000 debt.

You’ll greatly reduce the term of the debt by making fixed payments every month. At $100 a month (2 percent of the initial debt), you’ll repay $5,000 in about seven years (which is still pretty long to pay for a Twinkie).

The free calculators at myvesta.org will show you how long it might take to pay off your own current debts.

If you’ll be using your credit card this summer for a trip abroad, check the fees before you go. An increasing number of banks are adding 2 percent to your overseas bills, McKinley says.

McKinley also advises you to tell your card issuer if you’re going abroad. Otherwise, its fraud-alert system might block your card if you use it more than a limited number of times a day.

That happened to me three years ago when I was in Asia. The second time I used a particular MasterCard, it didn’t go through. I used a different card successfully for the rest of the trip. That card simply required me to produce extra identification from time to time.

When I got home, I found a call from the MasterCard bank on my answering machine. The bank was asking for authorization to approve my blocked purchase.

The bank had frozen my card because it couldn’t find me. Of course it couldn’t find me! I was in Asia! Grrrr.

A larger percentage of people today are using their credit cards for daily purchases. Often, it’s purely for convenience or for frequent-flyer miles.

Convenience users pay off the debts at the end of the month. In 1998, 56 percent of families had no balance on any of their cards, according to the most recent survey by the Federal Reserve.

At the other end of the scale, however, a higher percentage of people are in far too deep.

You’re potentially in trouble, if your monthly debt repayments (including mortgage and auto loans) come to more than 40 percent of your monthly income.

In 1998, 12.7 percent of families had fallen into this hole, compared with 10.5 percent in 1995.

Syndicated columnist Jane Bryant Quinn can be reached in care of the Washington Post Writers Group, 1150 15th St., Washington D.C. 20071-9200.