My team landed on a process of breaking projects down into milestones and then tasks and being consistent with buffers for both internal and external parties.
As a side project, I actually built a tool to help with this: "Calculeeto" (http://calculeeto.herokuapp.com/). Besides walking you through the process of breaking down your project and adding buffer, it also has features to assign dependencies and generate a schedule based on number of teammates -- it even adds time for communication overhead: http://calculeeto.herokuapp.com/?debug4
I never launched or finished it but it seemed useful.
As a side project, I actually built a tool to help with this: "Calculeeto" (http://calculeeto.herokuapp.com/). Besides walking you through the process of breaking down your project and adding buffer, it also has features to assign dependencies and generate a schedule based on number of teammates -- it even adds time for communication overhead: http://calculeeto.herokuapp.com/?debug4
I never launched or finished it but it seemed useful.