The Next Chapter, page-993

That's penalty interest for late payment of your credit card and has nothing to do with SPT.

Your comment about Sneef is the only juvenile comment made here. You can't differentiate between penalty interest and the amount you pay when you pay your card off each month which explains why you don't understand the SPT model.

I assume you have a carry over balance on your credit card every month and think it is good financial management. Personally I don't pay interest on credit cards as they are just a convenient payment method and I pay the balance every month. SPT taps into this way of using your credit for bigger purchases and high quality credit customers.