I don't know how you're getting anything out of it, since the index isn't even being used.
You could do this:
vd_inc = 1:100;
p = zeros(1,5);
for index = 1:numel(p)-1
p(index+1)= p(index)+ vd_inc(31-index+1);
end
p
but you really don't even need the loop
p = [0 cumsum(vd_inc(31:-1:28))]
