It’s really simple — it has the fields of:
Annual % Interest
Years to Pay it Off
Then you can choose if you want it to solve for amount owed, monthly payments, or years to pay it off.
It was what I was looking for – really really simple — I could quickly find out how much sooner I could pay things off by adding just a little bit to the monthly payment number.
I sort of used the calculator for your question — and it’d be less than $5.