I have the following program which should count the number of years it should take a population to grow to the desired size. Whenever I run this I get an infinite loop. Can someone help me identify my error? 

```
def pop_growth(start, percent, desired)      
  year_count = 0
  while start <= desired    
    year_count += 1
    start = start + (start * (percent / 100))
  end
  return year_count
end

```