The Estimated Time to Complete (ETC) for a manually allocated project is calculated as follows:
ETC = Sum of (remaining days * allocated hours per resource)
For example, let's say today is July 1st, and the project's due date is July 10th. This gives us 9 remaining days. We have two resources working on the project:
Resource A is allocated 2 hours per day.
Resource B is allocated 3 hours per day.
The calculation would be:
ETC = (9 days * 2 hours/day for Resource A) + (9 days * 3 hours/day for Resource B)
ETC = (9 * 2) + (9 * 3)
ETC = 18 + 27 =45 hours
So, the total ETC is 45 hours.
In a nutshell, for ETC to not be zero, we need
1. Allocation for resources in the project.
2. Remaining days in the project.
Hence, the ETC must've been populated as zero either because the project was marked completed or because there are no remaining days and hence no allocations.