I have an android phone and found an app called “Pay Off your Debt! Calculator”

It’s really simple — it has the fields of:
Amount Owed
Annual % Interest
Monthly Payments
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.