while/for loops in deposit calculations

hello, i am trying to work out a problem that i am having with while loops. i have to determine how much to save each month in order to reach a goal of 100836 in 216 months. the interest rate is 5.5 per year. so far, i have written the following script but the number does not seem believable to me.

%minimum deposit in 18 years

n=18*12;

balance= 2000;

deposit=200;

while balance<100836.46

      balance=balance*(1+(5.5/1200))+deposit;
      deposit=deposit+50+(20*n);
  end

disp(deposit)

disp(balance)

i end up getting an odd number which is 35160. i think that the number should be in the 200's assuming that the initial deposit is 200.

[Star Strider]

Duplicate of: http://www.mathworks.com/matlabcentral/answers/252360-while-loops-with-compound-interest