Estimate to Completion (ETC) is what we expect to spend from this point forward, based on our performance up to now.
Calculated by taking the Budget At Completion and dividing it by the Cost Performance Index.
It is what we expect to have spent at the end of the project.
We already know the estimate at completion and we will work at the same rate
ETC = EAC – AC
Practically speaking, we will not know the EAC and will need a bottom-up ETC