Project Planned End Date Calculation?

[Edwin Fuller]

I understand the planned end date for a project is calculated using the below formulas. However, I can't find where the calculation is actually being done whether it be a client script or business rule. Can someone show me where to locate how the planned end date for a project is calculated?

Planned End Date = Planned Start Date + Planned Duration

or

Planned End Date = Actual Start Date + Planned Duration

[ColeM]

Edwin mentioned "I've checked the default value, and there's no default value."
I'm having the same issue even with no default value.  Any ideas what else could be causing this?