Seeking Amortization Tool with Special Abilities

[Stephanie Alexander]

Does anyone have a website or resource for calculating amortization schedules where you can input how a large lump sum would impact time & overall pay down of the loan, or how regular extra principle applied to the loan would impact time/pay down, etc? I used to have a mortgage with a bank that had this capability but they changed it and then sold my loan and I don't have access anymore anyways. I have looked everywhere and can't seem to find anything that has the same capabilities.