It is Thursday afternoon. Your finance partner drops by your desk, coffee in hand, and asks the question you have been dodging all week.
"So, are we still landing at budget?"
You glance at your spreadsheet. You have spent 60 percent of the money. The project is maybe 40 percent done. You know, deep in your gut, that the honest answer is "no," but you do not have a tidy number to say out loud. So you mumble something about "tracking closely" and promise to circle back.
Estimate at Completion (EAC) is the number that ends that mumbling. It is one of the most useful concepts in project financial management, and you do not need to enjoy finance to use it.
EAC is your best current forecast of what the entire project will cost by the time it is finished, based on what you know today.
Not what you planned to spend. What you now believe you will actually spend.
And when you are managing multiple projects across a portfolio, that distinction becomes even more important.
Why your original project budget stopped telling the truth
Your budget was a promise made by a past version of you who had less information.
That past you did not know the vendor would be late, or that the one person who understands the payments integration would be pulled onto a support fire for three weeks.
The budget was your best guess at the start. It is not a lie. It is just old.
Here is the trap most teams fall into. They compare money spent against money budgeted, and if there is budget left, they relax.
That comparison hides the problem.
You can have plenty of budget remaining and still be heading for a significant overrun, because "budget remaining" says nothing about how efficiently you are turning money into finished work.
EAC changes the question.
Instead of asking, "How much money do we have left?" you start asking, "Given how the work has actually gone so far, what will the total bill be?"
That is a much more useful question for a project manager. It is an even more important one for a PMO responsible for understanding the financial health of an entire portfolio.
The one insight behind Estimate at Completion
Strip away the acronyms and EAC rests on a single, almost obvious idea.
If the first part of the project cost more than you expected, the rest might too.
Past performance is often one of your best indicators of future performance. If your team has been slower and more expensive than planned for two months, hoping the next two months will magically be different is not a forecast. It is a wish.
The simplest performance-based EAC calculation assumes that the cost efficiency you have experienced so far will continue.
To calculate it, you need a few numbers:
- Budget at Completion (BAC): The total approved budget for the project.
- Actual Cost (AC): How much the project has actually cost so far.
- Earned Value (EV): The budgeted value of the work genuinely completed.
- Cost Performance Index (CPI): A measure of cost efficiency, calculated by dividing earned value by actual cost.
The standard cost-efficiency-based EAC formula is:
EAC = AC + (BAC - EV) / CPI
In plain English, take what you have already spent, estimate the cost of the remaining work using your current spending efficiency, and add the two together.
You can also express this particular forecasting approach as:
EAC = BAC / CPI
Both formulas produce the same result when you assume current cost efficiency will continue and CPI is greater than zero.
There is a more optimistic approach, too.
If you believe the early overruns were caused by one-time problems that will not repeat, you can assume the remaining work will be completed at its originally budgeted cost.
That formula is:
EAC = AC + (BAC - EV)
Neither approach is automatically right. The key is understanding why your project is over budget and whether those conditions are likely to continue.
That is where a little judgment becomes just as important as the math.
A worked example with real-feeling numbers
Let us walk through a project I will call the Customer Portal Rebuild.
It is a six-month effort with a total approved budget of $300,000.
We are at the end of month three. Here is where we stand:
- Total project budget (BAC): $300,000
- Planned Value (PV) at month three: $150,000
- Actual Cost (AC) so far: $165,000
- Work genuinely completed: 40%
- Earned Value (EV): $120,000
Notice the problem.
You have spent 55 percent of the budget to finish only 40 percent of the work. The two numbers have drifted apart, and that drift is the whole story.
Planned Value tells us that $150,000 worth of work was scheduled to be completed by this point. But only $120,000 worth of budgeted work has actually been finished.
So we have a cost problem and a schedule problem.
Let us focus on the cost problem first.
Step 1: Calculate earned value
If the full project has a budget of $300,000 and you have genuinely completed 40 percent of its scope, the earned value is:
EV = $300,000 × 40% = $120,000
That means you have completed work originally budgeted at $120,000.
Step 2: Calculate cost efficiency
You spent $165,000 to complete $120,000 worth of budgeted work.
Your Cost Performance Index is:
CPI = $120,000 / $165,000 = 0.727
In plain terms, every dollar you spend is buying you roughly 73 cents of budgeted progress.
That is not a great exchange rate.
Step 3: Forecast the remaining cost
There is still $180,000 worth of budgeted work to complete.
If your current cost efficiency continues, finishing that work will cost approximately:
Remaining cost = $180,000 / (120,000 / 165,000) = $247,500
Add the $165,000 already spent:
EAC = $165,000 + $247,500 = $412,500
Step 4: Compare your forecast with your original budget
Here is what the numbers tell us:
- Original budget: $300,000
- Estimate at Completion: $412,500
- Projected budget overrun: $112,500
- Projected overrun percentage: 37.5%
Your budget said $300,000.
Your current performance-based forecast says $412,500.
That is a projected overrun of $112,500, and you found it at month three instead of month six.
Now consider the alternative scenario.
If the problems that caused the early cost overruns are resolved and the remaining work can be completed at its original budgeted cost, your EAC becomes:
EAC = $165,000 + ($300,000 - $120,000) = $345,000
You now have two forecasts:
- $345,000: If the remaining work is completed at its originally planned cost.
- $412,500: If the current cost inefficiency continues.
The difference between those forecasts is $67,500.
That gap is worth a conversation.
Can you realistically improve efficiency? Are there vendor costs that will not repeat? Has the team overcome the problems that caused the early delays?
Or are you simply hoping things get better?
That is the real value of EAC. It turns a vague concern into a financial conversation grounded in actual performance and reasonable assumptions.
At month three, you still have room to adjust scope, address delivery problems, renegotiate with a vendor, or go to your sponsor with options.
At month six, you might only have an apology.
Where EAC gets complicated
EAC is a forecast, not a fact, and it depends heavily on the quality of the information behind it.
The biggest potential weakness is your estimate of how much work has actually been completed.
If someone reports "we are 40 percent done" when the real number is closer to 25 percent, your forecast will look much healthier than it should.
Teams do not necessarily overstate progress out of dishonesty. Sometimes they just underestimate how much work is left.
The last 10 percent of a project has a funny habit of taking longer than anyone expected.
That is why percent complete should be tied to actual deliverables, measurable milestones, or completed work whenever possible. Time elapsed is not the same thing as progress earned.
There are a few other limitations worth understanding.
Past performance does not always predict future performance. A project that struggled early because of an unusual setup cost or a temporary resource shortage may genuinely become more efficient. Your forecasting method should reflect what you reasonably expect to happen next.
EAC measures cost, not delivery dates. A project can be on budget and still be significantly behind schedule. Schedule performance needs to be evaluated separately.
EAC does not tell you whether the project is still worth completing. A project may exceed its original budget while still delivering substantial business value. Conversely, a financially healthy project might no longer support organizational priorities.
That last distinction becomes especially important when you move from managing individual projects to managing a portfolio.
Why EAC matters even more in project portfolio management
For one project, you can probably calculate EAC in a spreadsheet.
For 50 projects managed by different teams, the problem becomes much more complicated.
Each project manager may have a different way of measuring progress. Financial data might come from several systems. Resource costs change. Forecasts are updated inconsistently, and by the time leadership receives a consolidated report, some of the numbers are already outdated.
Now imagine your PMO trying to answer a few straightforward questions:
- Which projects are forecasted to exceed their approved budgets?
- What is the total projected cost of the portfolio?
- Which projects are experiencing worsening cost performance?
- Where should leadership intervene before overruns become unavoidable?
- Do projects with rising costs still justify their expected business benefits?
These are not just project accounting questions. They are portfolio management decisions.
And they are difficult to answer when every project lives in a separate spreadsheet.
This is where Project Portfolio Management (PPM) software becomes valuable.
Rather than treating EAC as an isolated calculation, a PPM platform can bring together project budgets, actual costs, forecasts, resource information, and portfolio reporting in one place.
That gives project managers and PMO leaders a more consistent view of financial performance across projects.
More importantly, it creates an opportunity to identify problems earlier and make informed decisions about where to invest, where to intervene, and where to reconsider priorities.
Connecting project costs to business value
There is another question that often gets lost when teams focus exclusively on budget performance.
Is the project still worth doing?
Imagine two projects with the same projected $100,000 budget overrun.
One is rebuilding a customer-facing system expected to deliver significant operational savings over several years.
The other is implementing a feature that no longer supports the organization's strategic priorities.
Financially, both projects have the same projected overrun.
Strategically, they may deserve very different decisions.
This is why cost forecasting becomes more useful when combined with benefits tracking and portfolio prioritization.
A rising EAC should not automatically mean canceling a project. But it should prompt a conversation about whether the expected benefits still justify the forecasted investment.
Perspective brings project and portfolio financial information together with benefits tracking, helping organizations evaluate not only what their projects are expected to cost, but also the value those projects are expected to deliver.
The goal is not simply to identify which projects are over budget.
It is to help leadership make better investment decisions with the information available today.
How to start using EAC this week
You do not need a sophisticated financial management process to get started.
Pick one project that makes you nervous. The gut feeling is usually a good detector.
Then follow these five steps:
- Gather your numbers. Identify your total approved budget, actual costs to date, and an evidence-based estimate of work completed.
- Calculate earned value. Multiply your total budget by the percentage of scope genuinely completed.
- Measure cost efficiency. Divide earned value by actual cost to calculate CPI.
- Forecast your final cost. Use your CPI to estimate the cost of the remaining work, or choose another EAC approach if the remaining work is expected to perform differently.
- Make a decision. Compare EAC with the approved budget and discuss the projected variance with your sponsor. Bring two or three possible responses, not just a warning.
Do this once a month for one project and you will already have a better financial picture than simply watching the remaining budget.
But once you are responsible for an entire portfolio, the discipline needs to scale.
That means consistent definitions, reliable cost data, regular forecasting, and visibility into how individual project changes affect the broader portfolio.
PPM software can help establish that consistency while reducing the manual effort required to consolidate financial information and prepare portfolio-level reports.
The math itself works just as well in a spreadsheet.
The difference is how efficiently you can apply it, how consistently teams use it, and how quickly leadership can act on what it reveals.
The bottom line
Your original project budget tells you what you expected to spend.
Estimate at Completion tells you what you currently expect to spend.
Neither number is useful if nobody acts on it.
A good EAC forecast will not prevent every overrun, but it can give you something almost as valuable: enough warning to do something about it.
And when you are managing a portfolio of projects, that early warning can be the difference between reacting to financial problems and actively managing them.
The budget tells you what you hoped. EAC tells you what you owe reality.