Does adding developers increase the hours?
I estimated the project to take 600 hours on my own and was asked what it would look like to add another developer. Looking at the tasks I chose some which would be best to be worked on independently and tried to avoid overlap in needs (don’t want someone building an interface if the underlying business objects aren’t complete). In the end I put the hours at 750, but the benefit is that the project gets done sooner in calendar days. This means I added about 25% more man hours due to the changes in approach wrought by the resource addition. This worked under the assumption that the second developer had skills commensurate with mine and that the project tasking stayed the same. I believe this number slides down with time and other factors such as whether or not the two resources were in the same location, had worked together before etc.
My question is this – is 25% overkill?
Not enough? What other factors am I not considering?
Does this number go down with longer projects?
What does a third person do?
Any advice would be appreciated.