Looking for a complex Mortgage Calculator

[Nate Crump]

Hey there, I was wondering if there is such thing, on a website or if it could be done on a spreadsheet, as a mortgage calculator that will account for sporadic and differing extra payments.

I have one where you can "add $500 to your monthly payment" or "add $5,000 to your yearly payments", and see how soon you would pay it off... but is there any way to see try and calculate your early pay off if you add $500 here and $4,000 there, then $2,500 there, etc?

It's really just for fun, but I would appreciate any ideas! Thanks.