The estimate to complete is the most honest number on a project — and the easiest one to fake. It answers a single question: how much money is left to spend to finish the work? Not the total cost. Not the final margin. Just what's left.
Finance directors quietly care about estimate to complete more than the total-cost number it feeds into. The total tells you where you'll land. The ETC tells you what's still at risk between now and delivery. That's the number you can still act on.
The problem is that most teams calculate ETC with a formula, rubber-stamp it, and move on. That formula hides trouble a real conversation would expose. Let's fix that.
ETC is what's left — EAC is where you land
Two acronyms travel together. Keep them straight.
Estimate to complete (ETC) is the forecast cost of the remaining work. Estimate at completion (EAC) is the full forecast: what you've already spent plus your ETC. So EAC = actual cost to date + ETC.
The math is trivial. The insight is not. A finance lead reviewing a portfolio doesn't want to know that a project will finish at $210K against a $200K budget. That's a post-mortem. They want to know that with $60K of budget left, the team genuinely needs $80K to finish. That $20K gap is the alarm — and it lives inside the ETC, not the EAC.
NetSuite's overview of project accounting concepts and business calculations walks through how these forecasts feed each other. The takeaway for operators: track the forward-looking number, because the backward-looking one arrives too late to change anything.
The formula-based shortcut that hides the fire
Here's how most project software calculates ETC by default. It takes your budget, subtracts what you've spent, and calls the difference your estimate to complete.
ETC = budget − actual cost to date.
Read that again. This formula assumes the remaining budget is the remaining cost. It has no opinion about the actual work left. If you budgeted $200K, spent $140K, the formula insists you have exactly $60K of work remaining — no matter how the project is actually tracking.
That's not a forecast. It's a restatement of the budget.
A slightly better version weights the ETC by performance to date, using a cost-performance index. It's more defensible, but it still projects the past forward. If your first phase ran hot for reasons that won't repeat, the formula punishes the whole project. If it ran cheap because the hard work is still ahead, the formula gives you false comfort. As Deltek's primer on project accounting notes, forecasts are only as good as the assumptions feeding them — and a formula makes those assumptions invisible.
Bottom-up ETC forces the honest question
The fix is to stop deriving ETC from the budget and start building it from the work.
A bottom-up estimate to complete asks the delivery lead one uncomfortable question: forget the budget — how much will it actually cost to finish from here? Then you rebuild the number task by task, hour by hour, from where the project truly stands today.
Run it like this:
- List the remaining scope. Not the plan from kickoff — what's genuinely left, including the rework nobody logged.
- Assign hours and rates. Use your real blended labor cost rate, not the rosy one from the proposal.
- Add known non-labor costs. Subcontractors, licenses, travel still to come.
- Compare to remaining budget. If your bottom-up ETC exceeds it, you've found the overrun while you can still do something.
Scoro's beginner's guide to project accounting makes the same point in gentler language: the value is in the review, not the arithmetic. The number is a byproduct. The conversation is the product.
The gap between the two numbers is your early warning
Run both methods and watch the spread. When formula-based ETC and bottom-up ETC agree, the project is honest. When they diverge, you've found the fire before it reaches the boardroom.
Picture a $200K engagement, $140K spent, 60% of scope delivered. Formula says $60K to finish. But your team is only 60% done and has already burned 70% of the budget. Bottom-up ETC, built from actual remaining tasks, comes back at $85K. The formula was hiding a $25K overrun behind a comforting subtraction.
That $25K is recoverable today. You can rescope, renegotiate, or reassign. In four weeks, it's a loss you explain in a partner meeting. This is exactly the kind of forward signal that separates firms that protect margin from firms that report on it — a theme Harvard Business Review returns to in what professional service firms must do to thrive.
Wire ETC into your monthly rhythm
ETC only works as a habit. Calculated once at kickoff, it's a guess. Refreshed every close, it's a control.
Tie it to the numbers you already track. Your project margin calculation is only trustworthy if the cost side reflects a real ETC, not a budget echo. The same goes for revenue recognition — a stale ETC distorts your work-in-progress accounting and your unbilled revenue figures, because both lean on percent-complete assumptions that a bottom-up review would correct.
Watch it alongside the ratios that drive delivery health. NetSuite's rundown of consulting KPIs that matter now puts cost-to-complete forecasting next to utilization for a reason: an ETC that assumes people you don't actually have available isn't a forecast, it's a wish. And for firms formalizing this into practice standards, the AICPA & CIMA firm practice management resources cover the review discipline that makes it stick.
Two practical anchors:
- Model the finish line with a margin calculator using bottom-up ETC, and pressure-test it against the break-even point for the engagement.
- Review every project where the two ETC methods diverge by more than 10%. That's your at-risk list.
For the full picture, the project costing hub and the broader professional services finance guides connect ETC to pricing, staffing, and billing.
The takeaway
Estimate to complete is a conversation dressed up as a formula. The formula version subtracts spend from budget and tells you what you already assumed. The bottom-up version rebuilds the cost to finish from the work still on the table — and forces the honest question of whether the remaining budget can carry it.
Run both. Trust the gap. That spread is the earliest, cheapest warning you'll get that a project is about to run over. Lead with the number, then have the conversation.
