Loan Amortization Schedule Calculator

I wanted a loan amortization schedule that would give a monthly breakdown of savings from extra principal payments made during the repayment stream and I also wanted it to be mobile friendly. I haven't seen any that meet my 1st requirement, and many don't meet the 2nd. So I wrote a little javascript program to compute loan amortization schedules, https://www.allensw.com/loancalc/.