ETC (Estimate to Complete)
ETC (Estimate to Complete) is the expected cost of finishing the remaining work. By definition ETC = EAC − AC; the canonical formula is (BAC − EV) ÷ CPI.
How it is computed
ETC (Estimate to Complete) is the expected cost of finishing the remaining work. Its relationship to EAC is the definition itself: ETC = EAC − AC, the final forecast minus what has already been spent. The canonical formula is (BAC − EV) ÷ CPI — the remaining value divided by cost efficiency to date. With a $1M budget (BAC), $400k earned (EV), and CPI at 0.8, ETC is ($1M − $400k) ÷ 0.8 = $750k: the remaining work is nominally worth $600k, but at current efficiency it will cost $750k.
Why it matters
Management's question is rarely "how much have we spent" and usually "how much more will this take." Funding plans and requests for additional budget rest on ETC. It is also the unit of re-estimation: when performance to date no longer represents what lies ahead, teams skip the formula, re-estimate the remaining work bottom-up as a new ETC, and rebuild the forecast as EAC = AC + ETC.
Common misconceptions
Treating the optimistic formula BAC − EV as the default is a frequent mistake. It assumes the remaining work will run exactly at planned efficiency (CPI = 1.0), so on a project that has been overrunning it systematically flatters the forecast — it is only defensible when the variance so far traces to a one-off event. ETC is also not the remaining budget (BAC − AC): remaining budget is the money available, ETC is the money likely to be needed. The indicator that asks how hard you must work to close that gap is TCPI.
wbsgantt has no cost axis and does not compute ETC; the scale of remaining work shows through progress and the CPM-recomputed schedule of what is left.