BAC vs EAC Explained: How to Forecast and Control Project Costs

Managing project costs isn’t just about tracking what you’ve spent. It’s about knowing where you’re headed and whether you’ll land within budget.

Two metrics make that possible: Budget at Completion (BAC) and Estimate at Completion (EAC). BAC tells you what you planned to spend. EAC tells you what you’re actually going to spend based on how the project is performing right now.

Understanding the difference between them helps you forecast accurately, spot trouble early, and make informed decisions before small variances turn into major overruns.

Whether you’re preparing for the PMP exam or managing a live project, knowing how BAC and EAC work together is essential for staying in control of your budget.

TL;DR

BAC is your original approved budget. EAC is your revised forecast based on actual performance. The gap between them shows whether you’re on track or heading for a cost overrun. Mastering both helps you forecast and control costs with confidence.

What Are BAC and EAC in Project Management?

Before you can compare BAC and EAC, you need to understand what each one measures and how they fit into earned value management.

These aren’t abstract formulas. They’re practical tools that help you answer a simple question: Will this project finish on budget?

What Is BAC (Budget at Completion)?

BAC is the total approved budget for your project. It’s the sum of all planned costs across every task, phase, and deliverable.

You establish BAC during project planning, and it becomes your cost baseline. Once approved, BAC stays fixed unless there’s a formal scope change or re-baseline.

Think of it as your financial target. If your project plan says the work will cost $500,000, that’s your BAC. It doesn’t change just because actual costs start running higher than expected.

What Is EAC (Estimate at Completion)?

EAC is your updated forecast for what the project will actually cost by the time it’s done. Unlike BAC, EAC changes as the project progresses.

It’s calculated using actual performance data like how much you’ve spent, how much work you’ve completed, and how efficiently you’re using your budget. EAC gives you a realistic view of where you’re headed financially.

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BAC vs EAC: Key Differences Explained

Understanding how BAC and EAC differ helps you use them correctly. They serve distinct purposes in cost management, and knowing when to rely on each one makes forecasting more accurate.

Definition and Purpose

BAC represents your planned total cost. It’s what you committed to at the start based on estimates and assumptions. EAC represents your forecasted total cost based on how the project is actually performing.

BAC is your target. EAC is your reality check.

Timing of Use

You set BAC at project initiation once the budget is approved and the cost baseline is established. It reflects your best estimate before any work begins.

EAC evolves throughout the project. You recalculate it regularly as new cost and performance data becomes available. The further along you are, the more accurate your EAC should become.

Responsibility

BAC is approved by project sponsors or stakeholders during the planning phase. It requires formal sign-off because it sets the financial boundary for the project.

EAC is updated by the project manager based on earned value analysis. You’re responsible for tracking performance and revising the forecast as conditions change.

Change Dynamics

BAC remains static unless there’s a scope change, approved change request, or formal re-baseline. You don’t adjust it just because costs are running high.

EAC is dynamic. It shifts with every reporting period as actual cost, earned value, and cost performance index change. It’s meant to reflect current trends, not original plans.

Example Summary

If your BAC is $1 million but your EAC climbs to $1.2 million, you’re forecasting a 20% cost overrun. That gap between BAC and EAC signals the need for corrective action or stakeholder communication before the situation worsens.

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How to Calculate BAC and EAC in Project Management

Knowing the formulas behind BAC and EAC helps you apply them correctly and interpret the results with confidence. These calculations aren’t complicated, but they require clean data and an understanding of when to use each approach.

BAC Formula

BAC is straightforward. Add up the cost estimates for all planned work in your project:

BAC = Σ (Cost Estimates for All Tasks)

If your project includes design ($50,000), development ($120,000), and testing ($30,000), your BAC is $200,000. That’s your cost baseline.

EAC Formulas

EAC has multiple formulas depending on what’s driving your variance and what assumptions you’re making about future performance:

1. EAC = BAC / CPI (use when cost variance is the primary issue and you expect current performance trends to continue)
2. EAC = AC + (BAC – EV) (use when past performance was unusual and future work will proceed as planned)
3. EAC = AC + [(BAC – EV) / (CPI × SPI)] (use when both cost and schedule variances are affecting the forecast)

Worked Example

Assume your project has a BAC of $200,000. You’ve completed work worth $90,000 in earned value (EV) but spent $100,000 in actual cost (AC).

Using the formula EAC = AC + (BAC – EV):

EAC = 100,000 + (200,000 – 90,000) = $210,000

Interpretation: Your project is now forecasted to exceed its initial budget by $10,000. You’re trending toward a cost overrun, and that’s your signal to investigate causes and consider corrective actions.

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How to Use BAC and EAC for Cost Forecasting

EAC isn’t just a number you calculate for reporting. It’s a forecasting tool that helps you maintain visibility into project finances and take action before small problems become major budget failures.

Forecast Accuracy

As your project progresses and you gather more actual cost data, your EAC becomes more reliable. Early in the project, your forecast might swing based on limited information.

But by the time you’re halfway through, performance trends stabilize and your EAC gives you a realistic picture of where you’ll land financially. Regular updates keep your forecast grounded in reality, not wishful thinking.

Variance Analysis

Comparing EAC to BAC tells you whether you’re trending toward an overrun or underrun. If EAC exceeds BAC, you’re forecasting a cost overrun. If EAC is lower than BAC, you’re on track to finish under budget.

This variance becomes the basis for status reports, stakeholder updates, and risk assessments. It shows whether your cost performance is improving, stable, or deteriorating.

Management Response

When EAC signals trouble, you have options. You can adjust resource allocation, renegotiate scope, accelerate certain tasks to improve efficiency, or request additional funding.

In some cases, you might re-baseline the project if the variance is significant and approved by stakeholders. The key is using EAC insights proactively, not waiting until the budget is already blown.

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BAC vs EAC Comparison Table

Here’s a side-by-side comparison to clarify how BAC and EAC differ in purpose, timing, and application:

Interpretation: BAC anchors your cost expectations. EAC reflects your financial reality as the project unfolds.

When EAC drifts away from BAC, you know performance isn’t matching the plan. The wider the gap, the more urgent your need for corrective action.

This table gives you a quick reference for understanding when and how to use each metric in earned value management.

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Example Scenario: Applying BAC and EAC in a Real Project

You’re managing a software development project with a BAC of $500,000. Halfway through, the client requests additional features that weren’t in the original scope.

Your team agrees to the change, but it impacts both timeline and cost. You run the numbers using earned value data.

Your actual cost (AC) is now $280,000, but earned value (EV) is only $240,000. Your cost performance index (CPI) sits at 0.86, meaning you’re getting 86 cents of value for every dollar spent.

Using the formula EAC = BAC / CPI, you calculate:

EAC = 500,000 / 0.86 = $581,395

This forecast shows you’re trending toward an $81,395 overrun.

Armed with this insight, you update stakeholders immediately, discuss options for scope adjustment or additional funding, and document the variance in your status report.

Without recalculating EAC, you wouldn’t have spotted the financial drift until it was too late to respond effectively.

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Common Mistakes When Comparing BAC vs EAC

Even experienced project managers make avoidable errors when working with BAC and EAC. Here are the most common pitfalls:

Confusing baseline with actuals: BAC is your planned budget. EAC is your forecast. Treating them as interchangeable muddies your financial picture and undermines decision-making.

Ignoring performance trends before revising EAC: Don’t wait until variances are severe. Recalculate EAC regularly so you catch cost drift early, not after the damage is done.

Treating EAC as static instead of iterative: EAC should evolve as new data comes in. A stale forecast misleads stakeholders and delays corrective action.

Not documenting changes or assumptions in forecasts: When you update EAC, record why. Document what changed, which formula you used, and what assumptions you’re making about future performance. Without that context, your forecast loses credibility.

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FAQs

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Key Takeaways

BAC represents your planned total project cost and serves as the cost baseline. EAC is your updated cost forecast based on actual performance trends. Compare both regularly to monitor financial health and spot variances early.

When EAC exceeds BAC, you’re forecasting a potential overrun that requires corrective action. Continuous tracking through earned value management ensures you stay proactive rather than reactive.

Use the right EAC formula based on your project’s performance patterns, and document your assumptions every time you update the forecast.

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Earned Value Management Glossary

BAC (Budget at Completion): Total authorized budget baseline for all project work.

EAC (Estimate at Completion): Updated cost forecast based on current performance.

CPI (Cost Performance Index): Ratio of earned value to actual cost, measuring cost efficiency.

EV (Earned Value): Value of work actually completed.

AC (Actual Cost): Total cost incurred for work performed.

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