calculate budget at completion

What Is Budget at Completion (BAC)?

Budget at Completion (BAC) is the total approved budget for the full scope of a project. In earned value management (EVM), BAC is one of the anchor values used to measure cost performance, forecasting, and control. If you know your BAC, you can quickly calculate other core metrics like cost variance at completion, estimate to complete, and performance-based forecasts.

In many organizations, BAC is established during baseline planning and approved before execution starts. However, people often still need to “calculate BAC” in the field when they only have partial data (for example, EV and percent complete, or AC and ETC). That’s exactly why this calculator includes multiple practical methods.

How to Calculate BAC

Method 1: Using Earned Value and Percent Complete

If your earned value is known and your physical progress estimate is reliable:

BAC = EV / (% Complete / 100)

Example: EV = $42,000 and project is 35% complete:

BAC = 42,000 / 0.35 = $120,000

Method 2: Using Actual Cost and Estimate to Complete

If you know what you have spent and what you still expect to spend:

BAC = AC + ETC

Example: AC = $50,000 and ETC = $70,000:

BAC = 50,000 + 70,000 = $120,000

Method 3: Using EAC with CPI Adjustment

If EAC is available and you want to infer BAC based on current cost efficiency:

CPI = EV / AC
BAC = EAC × CPI

This method is useful in advanced forecasting scenarios, though it depends heavily on the quality of CPI and forecasting assumptions.

Quick Reference Table

Formula	Use When	Watch Out For
BAC = EV / %Complete	You trust progress measurement	Biased or subjective % complete
BAC = AC + ETC	You have updated remaining cost estimate	ETC may be stale or optimistic
BAC = EAC × CPI	Forecasting with performance trends	CPI may not remain stable

Why BAC Matters for Project Control

• Baseline discipline: BAC defines the financial target for the project scope.
• Forecasting: BAC interacts with EAC and VAC to signal potential overruns early.
• Performance interpretation: BAC helps frame CPI and SPI trends in business terms.
• Stakeholder communication: It creates a clear reference point for executives and sponsors.

BAC and Related EVM Metrics

Estimate at Completion (EAC)

EAC is your current best estimate of total project cost when all work is done. If EAC rises above BAC, you are forecasting an overrun.

Variance at Completion (VAC)

VAC = BAC − EAC. A negative VAC indicates a projected budget overrun. A positive VAC indicates projected underrun.

Cost Performance Index (CPI)

CPI = EV / AC. CPI below 1.00 means cost inefficiency; above 1.00 means cost efficiency.

Estimate to Complete (ETC)

ETC is the expected remaining cost from now to project finish. If BAC and AC are known, a simple baseline ETC can be estimated with ETC = BAC − AC (before performance adjustments).

Common Mistakes When Calculating BAC

• Using subjective percent complete values without objective measurement criteria.
• Mixing baseline numbers with forecast numbers without documenting assumptions.
• Forgetting that BAC should represent approved scope at baseline, not ad-hoc scope growth.
• Using CPI-based BAC back-calculations without checking whether performance is stable over time.
• Ignoring change control: major approved changes should trigger baseline review and potential BAC re-baselining.

Best Practices for Better BAC Accuracy

1. Use objective progress rules (0/100, 50/50, weighted milestones) where possible.
2. Update ETC with fresh data from engineering, procurement, and operations teams.
3. Separate one-time anomalies from recurring performance trends before relying on CPI.
4. Reconcile BAC, EAC, and scope changes in a regular monthly cost review.
5. Document assumptions behind every forecast and keep version history.

Practical Example

Suppose a project manager reports EV of $84,000 at 60% completion. Method 1 gives:

BAC = 84,000 / 0.60 = $140,000

If AC is currently $95,000 and EAC is forecast at $155,000, then:

• VAC = BAC − EAC = 140,000 − 155,000 = −15,000
• The project is currently forecast to exceed budget by $15,000.

This type of analysis gives teams time to implement corrective actions before final delivery.

Final Thoughts

When people search for “calculate budget at completion,” they are usually trying to answer one of two questions: “What is our true budget baseline?” and “Are we likely to finish over or under budget?” A clean BAC calculation, paired with EAC, CPI, and VAC, gives a fast and reliable decision framework. Use the calculator above regularly during status reviews to keep your forecasts honest and your project financially healthy.