Question

If a store credit account charges 1.5% interest each month, what is the APR?

Answer 1

If the monthly interest is 1.5%, then the APR is

100 [ (1.015)¹² - 1 ] = 19.56 %

You might think that it would be (12 x 1.5) = 18% , but it's not.

The interest is compounded.  That means interest is added this month,
and then it becomes part of the amount on which interest is charged
next month.

So you're charged interest on interest, and it adds up.

Answer 2

The APR is the annual percentage rate
therefore the APR is 1.5x12=18%