EAC Project Management: Estimate at Completion Guide
What is EAC in project management?
EAC in project management means Estimate at Completion. It is a forecast of the total cost of a project when all approved work is finished. Project managers use EAC to compare the original budget with the likely final cost after actual cost, earned value, and current performance are known.
Estimate at Completion is useful because the original budget rarely stays perfectly accurate throughout a complex project. Scope changes, slower progress, rework, vendor delays, and staffing changes can all affect the final cost. EAC gives the project team and stakeholders a structured way to update the forecast instead of relying on optimism or a rough guess.
PMI describes earned value as a practical way to connect scope, schedule, and cost performance. EAC belongs in that same earned-value reporting system because it turns current performance into a forward-looking cost forecast. For background, see PMI's article on making earned value work on projects: How to make earned value work on your project.
EAC formula project management terms
| Term | Meaning | Role in EAC |
|---|---|---|
| AC | Actual Cost, or what the project has spent so far. | Shows the real cost already incurred. |
| EV | Earned Value, or the budgeted value of completed work. | Shows how much planned work has been earned. |
| BAC | Budget at Completion, or the original total approved budget. | Provides the baseline final budget. |
| CPI | Cost Performance Index, calculated as EV / AC. | Shows current cost efficiency. |
| SPI | Schedule Performance Index, calculated as EV / PV. | Adds schedule efficiency when future cost depends on schedule performance. |
| ETC | Estimate to Complete, or the expected cost of remaining work. | Can be added to AC to create EAC. |
These inputs need consistent measurement rules. If teams overstate percent complete, classify costs late, or change the baseline without documenting it, the EAC calculation will look precise while still being unreliable.
Common EAC formulas
There is no single EAC formula for every project. The right formula depends on what you believe about the remaining work.
| Scenario | Formula | Use when |
|---|---|---|
| Future work will follow the original plan | EAC = AC + (BAC - EV) | Past variance is unusual and remaining work should perform as planned. |
| Current cost performance is expected to continue | EAC = BAC / CPI | Cost efficiency so far is a good predictor of remaining work. |
| Cost and schedule performance both affect remaining work | EAC = AC + ((BAC - EV) / (CPI * SPI)) | Delays are likely to affect remaining cost as well as schedule. |
| A new bottom-up estimate exists | EAC = AC + ETC | The team has re-estimated the remaining work directly. |
The formula is less important than the assumption behind it. A project manager should explain which formula was used and why that assumption fits the current project.
How to calculate EAC
Use this process to calculate EAC in a way stakeholders can review.
- Set the status date: Use the same reporting date for AC, EV, CPI, and SPI.
- Confirm BAC: Check the approved budget at completion after any approved scope changes.
- Measure actual cost: Pull actual cost from the financial system or approved project cost report.
- Measure earned value: Count only work completed by agreed completion rules.
- Choose the formula: Select the formula that matches the performance pattern.
- Explain the assumption: State whether the forecast assumes planned performance, current cost performance, combined cost/schedule performance, or a new bottom-up estimate.
- Compare EAC with BAC: Show whether the project is forecast to finish under, on, or over budget.
EAC calculation example
Assume a project has:
| Input | Value |
|---|---|
| Budget at Completion (BAC) | $500,000 |
| Actual Cost (AC) | $260,000 |
| Earned Value (EV) | $225,000 |
| Cost Performance Index (CPI) | 0.87 |
If the project manager believes current cost performance will continue, the formula is:
EAC = BAC / CPI
EAC = $500,000 / 0.87 = $574,713
The forecast says the project may finish about $74,713 over the original budget. That number should trigger a practical review: which work packages are driving the cost variance, which scope decisions are still open, and whether the remaining work can realistically be completed at a better cost rate.
EAC vs ETC vs BAC
EAC, ETC, and BAC are related, but they answer different questions.
| Metric | Question it answers |
|---|---|
| BAC | What was the approved total budget? |
| ETC | What will the remaining work cost from today forward? |
| EAC | What will the whole project cost at completion? |
| VAC | How far is the forecast from the original budget? |
Variance at Completion is calculated as:
VAC = BAC - EAC
If VAC is negative, the project is forecast to finish over budget. If VAC is positive, it is forecast to finish under budget.
When EAC improves project decisions
EAC helps most when project leaders need to make decisions before the project is already over budget.
Use EAC to:
- update stakeholders when actual costs no longer match the original budget
- decide whether to reduce scope, add budget, or change delivery sequencing
- compare budget pressure across a portfolio
- connect cost forecasts with schedule metrics like SPI in project management
- decide when a project needs a formal reforecast instead of a small correction
Scrumbuiss can support this kind of review by keeping project status, ownership, risks, timelines, files, and reporting context visible in one workspace. The financial calculation may still come from your finance system, but the delivery signals behind the forecast need to be visible to the project team.
EAC reporting best practices
Good EAC reporting is clear about the number and the reason behind the number.
Include these fields in an EAC update:
- original BAC
- current AC, EV, CPI, and SPI
- selected EAC formula
- current EAC forecast
- variance at completion
- top cost drivers
- corrective action
- owner and review date
For example:
Current EAC is $574,713 against a BAC of $500,000, creating a forecast overrun of $74,713. The forecast uses
EAC = BAC / CPIbecause current cost performance has been consistent across the last two reporting periods. The main driver is integration rework. The team will review scope options and vendor support before the next steering meeting.
That update is easier to trust than a single number because it states the method, cause, and next action.
Common EAC mistakes
Using one formula for every project
Different formulas answer different assumptions. A stable project with one unusual cost spike should not always use the same formula as a project with a repeated cost-efficiency problem.
Ignoring schedule pressure
If delays increase labor cost, expedite fees, or vendor cost, schedule performance can affect the final cost. In that case, a formula using CPI and SPI may be more useful than a cost-only formula.
Updating EAC without explaining why
Stakeholders need to understand why the forecast changed. Tie EAC changes to scope, cost rate, rework, staffing, vendor, or schedule factors.
Treating EAC as a punishment metric
EAC should help teams make better decisions. If teams fear reporting a worse forecast, they may delay the update until recovery options are limited.
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