I am making a mortgage spread for an adjustable rate mortgage. Every row is a
month, 1-360. I am adding a spread percentage (2.25%) to a base percentage
(LIBOR, if you know what I am talking about) to get the interest rate for the
mortgage . The base percentage is changing every 12 months using this
formula:

=IF(MOD(A76,12)<1,B75,(RANDBETWEEN(4,10)+RAND())/100)

The interest rate cannot change more than 3% in a year and cannot change
more than 6% from the starting rate (meaning it can't go below 0 or above 12)
in the life of the loan . For example if the base percentage is 10%+spread
(2.25%)=12.25%. This is above the max cap of 12%, so the formula needs to
make it 12%. Also, if the year before the base percentage was, say, 4%, then
4%+2.25%=6.25%. The interest rate can't change more than 3% in a year,
though, so the formula needs to take this cap into account; in this situation
it should say 9.25%. Since for the project I have to randomly generate base
percentages, the formula has to have these caps in it.

I hope I have been clear enough. Any suggestions?