Why does RCDC give me more rebar than Necessary

Good day, I tried using RCDC 9.2 for my concrete design and it is over reinforcing my beam section. 

I have a single span beam of 6m with a property of .23X.45. and a mid-span moment of 90kNm

from my manual design, I am getting 4Y16. but rcdc is giving me 5Y16 why?

from RCDC