Where can I find one I advanced calculator loan amortization?

I need a calculator or a spreadsheet of amortization the loan that will allow me to enter graduate payments (eg 12 months $ 50 followed by 36 months @ $ 100, etc..) I'm trying a table and graph payment plan for my student loans. The online calculators I found you a serial input of payments.

I not aware of any amortization calculators good as the one you mentioned in line (although I wish there was!) I had become very good at using Excel to creat this kind of thing. It is certainly possible to do with Excel.