WASHINGTON — Helen Galanoplos tried to cancel her American Express card last year because she no longer wanted to pay an annual fee. But, she said, the customer service representative told her that her credit score could go down as a result.

Then last week, she received a letter from Chase notifying her that her credit card was to be canceled because she had not used it in two years. The bank said it would forward that information to the companies that produce credit reports.

A retiree who does not believe in carrying a credit-card balance, she has made it a habit to pay off her cards in full each month. (She also has a Capital One card.) So she didn't understand why her score would go down.

"I'd appreciate some clarity as to these baffling actions," wrote Galanoplos, a Washington resident and former personal secretary to three members of Congress. "If I pay in full, whether $30 or $3,000, why is my credit rating threatened?"

It turns out that there are quite a few people out there who have had their credit cards canceled because of lack of use. I had it happen with one of my own credit cards recently. For those looking to buy homes or get loans, it can be a real problem because banks these days are loath to lend to people with credit scores below 700.

Unfortunately, it's not so easy to figure out how your credit score would be affected by a credit card company cutting you off.

Let's look first at the factors that can affect FICO credit scores, which are calculated by Fair Isaac Corp.

u Payment history, which shows if you've missed payments or have had any bankruptcies or any liens against you, counts for 35 percent.

u Amounts owed, which shows among other things the proportion of credit lines used (often referred to as your credit utilization ratio, essentially telling you how maxed out you are), counts for 30 percent.

u Length of credit history counts for 15 percent.

u New credit, which includes the number of recent credit inquiries, is 10 percent.

u Types of credit used is the final 10 percent.

A few things that do not go into your credit score are your age, salary and interest rates charged on your credit cards.

(For more information on how your FICO score is calculated, go to www.myfico.com.)

Now, it is hard to say exactly what the two situations Galanoplos is facing will do to her credit score without looking closely at her credit report. And even then, how a FICO score is produced will depend on a variety of factors. I talked to a couple of experts about it. Here's what they had to say.

First, consider her American Express card. She decided to hold on to it last year because, she said, the company waived her annual fee. But as a retiree, she's wondering if she needs so much credit. "I don't do a lot of shopping at my age anymore," she said.

In general, American Express poses a problem in calculating FICO scores because cardholders typically don't have limits. Craig Watts, a spokesman for Fair Isaac, said that because no credit limit is reported, the company tries to substitute it with the highest balance on record for that card. But sometimes that's not available. When it's not, the account is not used at all in calculating the credit utilization ratio, Watts said.

In other words, we don't know if losing that American Express card would affect her score because we don't even know if it's being counted.

Now let's look at the Chase situation. Watts said it probably won't matter.

"In her case, because her card was so unused for so long, it's unlikely the FICO score was using it to calculate her credit score," he said.

Watts said the best advice he can give any consumer is this: "Use your credit cards sparingly, always pay them off and keep those balances as low as you can."