Comment by Nokinside

Simple equation that is just as good as any:

p : number of people

c : number of changes into specifications (= learning during implementation)

f : number of frameworks, libraries, tools.

x : number of new people, frameworks, libraries, tools

e : initial time estimate in weeks

correct estimate: E = e + e(0.1p + 0.2c + 0.3f + 1.1^x)