ok,

i'm trying to make out an amortization table for a mortgage for one of my
classes. We have to amortize by the month for a 30 year mortgage. He gave us
the property tax percentage and said that it goes up by a certain percentage
every year. He wants to be able to drag the formulas down from the first row
all the way down and everything equal out to zero.

How do you program the formula so the taxes go up only every 12 months?
Like, 1-12 will be 3%, then 13-24 will automatically go up to 3.5%.

Any help will be greatly appreciated. Thanks!