What is the catch with “balance transfer” credit cards? [duplicate]

Question

This question already has an answer here:

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If I understand correctly I can transfer a balance of my credit card to a new credit card and pay no interest for 40 months?

How your promotional rates will change

After 40 months, the rate on Balance Transfers will go from 0% to 18.95%.

After 6 months, the rateon Purchases will go from 0% to 18.95%.

Fees to be aware of

For a balance transfer, you'll be charged 2.39% of the balance you're transferring.

Of course I should be super-vigilant to repay the money within 40 months period but still... How do they make money?

Answer 1

They immediately make money by charging you the initial 2.39% fee.

In the long term they make money because a surprisingly large number of customers don't pay the balance off, or otherwise violate the terms of the offer, so that the 18.95% rate applies.

And sometimes, depending on card policies, they make money when the consumer makes new purchases on the card which accrue interest immediately at the 18.95% rate while payments only go to paying down the 0% rate balance.