Interest rate is yearly not monthly. But let's say it is monthly to show how insane and illegal that is, 20 percent monthly interest instead of yearly and you borrow a hundred bucks at the end of a year you would owe 891.61 if you made no payments. That would make your interest rate 791 percent yearly.
Now of it's yearly interest like normal and by law but compounded monthly (which generally how credit cards do it) then you owe 121.94. So a 1.94 more than if interest was compounded yearly, so does add almost 2 percent more each year compounding monthly instead of yearly. Compounding simply means it calculates and charges your interest monthly so basically if you made no payments it's 1/12 of 20% (1.67%) multiplied to your remaining loan amount, so after a month you owe 101.67.
