What would you tell this man, who phoned yesterday for my thoughts on his credit card strategy?

He is a retiree who has been carrying $45,000 in card debt for three or four years. Although he has savings enough to pay the whole amount immediately, he has been shifting the debt from card to card to take advantage of introductory offers that waive interest charges on “balance transfers” for the first few months.

This way, he has avoided paying interest on the card debt. Meanwhile, money that could be used to pay the debt has instead been earning 8 percent to 9 percent a year in a variety of investments.

Is he clever?

Or crazy?

Too clever for his own good, in my view.

The first warning sign is the size of the debt. No person of modest means, as this reader is, should rack up $45,000 in credit-card debt – ever, under any circumstances.

Credit cards should be used only as a safe and convenient alternative to carrying cash. Ideally, you should not incur more debt than you can pay off by the end of the month, thus avoiding any interest charges. (OK, go a bit longer after the holidays or a vacation. But not more than two or three months.)

The second danger signal is habitually shifting the debt from card to card. That’s like pouring a drink while the last one is still half full – a sign of addiction.

Third, while the math behind this reader’s strategy looks sound on first glance, it’s a risky game of musical chairs.

The reader argues he comes out ahead by earning 8 percent to 9 percent on his investments. But to do that, one generally has to take some risk – by investing in stocks or stock mutual funds, for example.

What if the market plunges? The reader might be left with too little to pay off the card debt.

And the zero-percent introductory offers may stop coming. If so, the reader would be stuck paying the regular “go-to” card rates – 15 percent, 18 percent or 20 percent.

In addition, most zero-percent deals are salted with landmines. Make a payment late, for example, and the sky-high go-to rate may kick in immediately.

Generally, the zero-percent deal applies only to the balance transfer, while the go-to rate applies to debts incurred when the card is used for ordinary charges.

In most cases, any payments the borrower makes are first applied to the zero-percent portion of the debt. That means the high rates charged on new debts snowball until the transfer is paid off. In this case, the card user can end up paying interest upon interest upon interest.

Finally, the reader’s strategy overlooks the fact that the credit rating agencies know what he’s doing – they see everything.

Opening numerous card accounts, and frequently shifting money among cards without reducing the overall debt is a red flag that could hurt his ability to borrow money in the future.

After all, the card issuers don’t value customers who don’t pay interest. And lenders know from experience that people who use transfer after transfer after transfer to postpone paying off their debts often end up in a box and never pay what they owe. So lenders don’t want this kind of borrower.

In fact, this behavior with credit cards is likely to hurt one’s ability to get a mortgage or car loan as well.

Is there never a time when a balance transfer makes sense?

It might make sense if you’re in a temporary fix and do it once. Pick a card that waives interest on the transfer for at least six months. And look out for transfer fees – some cards have them, some don’t.

Once the transfer is done, work hard to reduce the debt. Don’t use the new card for new charges, else you’ll be paying high interest rates until the transfer is paid off.

And think twice before throwing out the old card. Your credit report looks better if you’ve had just one or two cards and used them responsibly year after year.