How to Calculate Budget at Completion (BAC) & Project Cost Calculator
An essential tool for project managers to understand original budgets, forecast final costs, and analyze project performance.
Enter the currency symbol for your project (e.g., $, €, £).
The total original planned budget for the entire project.
The total cost actually incurred for the work completed to date.
The value of the work actually performed to date.
The budgeted cost of the work that was scheduled to be completed by now.
What is Budget at Completion (BAC)?
Budget at Completion (BAC) is a fundamental concept in project management, specifically within Earned Value Management (EVM). It represents the total, original, and approved budget allocated for a project. Essentially, if you plan a project and determine it will cost $500,000 from start to finish, your BAC is $500,000. This figure is established during the planning phase and serves as the primary cost baseline against which project performance is measured.
It’s crucial not to confuse BAC with Estimate at Completion (EAC). While BAC is the original plan, EAC is a dynamic forecast of what the total project cost will likely be, based on performance to date. A project manager’s goal is often to keep the EAC at or below the BAC. This calculator helps you understand both metrics.
Key Formulas for Project Cost Forecasting
While the question is “how do you calculate budget at completion,” the reality is that BAC isn’t calculated mid-project; it’s the sum of all planned budgets set at the start. The more practical question for a running project is, “Based on my performance, what will my final cost be?” This is answered by calculating the Estimate at Completion (EAC). Several formulas help us forecast this final cost.
Core Performance Indices
- Cost Performance Index (CPI): CPI = EV / AC. This measures cost efficiency. A CPI less than 1 indicates a cost overrun (over budget), while a CPI greater than 1 indicates a cost underrun (under budget).
- Schedule Performance Index (SPI): SPI = EV / PV. This measures schedule efficiency. An SPI less than 1 means the project is behind schedule, while an SPI greater than 1 means it’s ahead of schedule.
Common EAC Formulas
EAC = BAC / CPI: This is the most common formula and assumes the current cost performance (or inefficiency) will continue for the rest of the project.EAC = AC + (BAC - EV): This formula is used when you assume that whatever caused a cost variance to date was a one-time event, and the rest of the project will proceed as originally budgeted.EAC = AC + [(BAC - EV) / (CPI * SPI)]: This is used for troubled projects where you need to account for the combined impact of both poor cost and poor schedule performance.
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| BAC | Budget at Completion | Currency (e.g., $) | Positive Value |
| AC | Actual Cost | Currency (e.g., $) | Positive Value |
| EV | Earned Value | Currency (e.g., $) | Positive Value |
| PV | Planned Value | Currency (e.g., $) | Positive Value |
| CPI / SPI | Performance Indices | Unitless Ratio | 0.5 – 1.5 |
For more advanced project tracking, you might consider exploring advanced earned value techniques to refine your forecasts.
Practical Examples
Example 1: Project Over Budget
A software development project has a BAC of $200,000. At the halfway point, the team has spent $120,000 (AC) but has only completed work valued at $90,000 (EV).
- Inputs: BAC = $200,000, AC = $120,000, EV = $90,000
- Calculation: CPI = EV / AC = $90,000 / $120,000 = 0.75
- Result (EAC): Using the primary formula, EAC = BAC / CPI = $200,000 / 0.75 = $266,667.
- Interpretation: The project is forecasted to be significantly over budget. The Variance at Completion (VAC = BAC – EAC) would be -$66,667.
Example 2: Project Under Budget
A construction project has a BAC of $500,000. After the first phase, $100,000 has been spent (AC), and the value of completed work is $110,000 (EV).
- Inputs: BAC = $500,000, AC = $100,000, EV = $110,000
- Calculation: CPI = EV / AC = $110,000 / $100,000 = 1.1
- Result (EAC): EAC = BAC / CPI = $500,000 / 1.1 = $454,545.
- Interpretation: The project is performing efficiently and is now forecasted to finish under the original budget.
Understanding these scenarios is key to effective project cost management.
How to Use This Budget at Completion Calculator
- Enter Currency: Start by entering the currency symbol for your project.
- Input Core Values: Provide the four key data points from your project’s performance measurement baseline: Budget at Completion (BAC), Actual Cost (AC), Earned Value (EV), and Planned Value (PV).
- Calculate Forecast: Click the “Calculate Forecast” button.
- Review Results: The calculator will instantly display the key performance indices (CPI, SPI), the forecasted Estimate at Completion (EAC), and other valuable metrics. The chart and table provide deeper insights.
- Interpret Forecasts: Use the different EAC values in the table to understand potential outcomes based on different assumptions about future performance.
Key Factors That Affect Final Project Cost
- Scope Creep: Uncontrolled changes or additions to the project’s scope are a primary cause of cost overruns.
- Inaccurate Estimates: If the initial BAC was based on poor estimation techniques, it was flawed from the start.
- Resource Costs: Unexpected increases in the cost of labor, materials, or equipment can significantly impact the final cost.
- Risk Events: Unforeseen problems or risks that materialize during the project often require additional funds to mitigate.
- Team Productivity: A team that performs more or less efficiently than planned will directly affect the CPI and the final EAC.
- Project Delays: Schedule delays often have cost implications, such as extended labor costs or penalties, which is why the SPI is also important. A good project timeline tool can help prevent this.
Frequently Asked Questions (FAQ)
BAC (Budget at Completion) is the static, approved budget set at the project’s start. EAC (Estimate at Completion) is a dynamic forecast of the final cost, calculated during the project based on actual performance.
Correct. There isn’t a mathematical formula in the same way as for EAC. The BAC is determined by summing up the costs of all planned project activities, often using techniques like parametric estimating or analogous estimating.
It means your project is over budget. For every dollar you have spent, you have earned less than one dollar’s worth of value.
You should only re-baseline and formally change the BAC when there has been a significant, approved change in the project’s scope. It should not be done simply because the project is performing poorly.
Different formulas represent different assumptions about future project performance. Choosing the right one depends on whether you believe past performance issues were anomalies or are likely to continue.
VAC is the difference between your original budget and your forecasted final cost (VAC = BAC – EAC). A negative VAC means you are projected to be over budget, while a positive VAC means you are projected to be under budget.
Yes. If your EV is higher than your PV, it means you are ahead of schedule. You have completed more work than you had planned to by this point in time.
EV is typically calculated as the percentage of work completed on an activity multiplied by that activity’s planned budget. For example, if an activity budgeted for $10,000 is 50% complete, its EV is $5,000.
Related Tools and Internal Resources
Enhance your project management skills with these related resources:
- Project Portfolio Management Guide: Learn how to manage multiple projects at once.
- Critical Path Method Calculator: Identify the longest stretch of dependent tasks and measure project duration.
- Work Breakdown Structure Tips: See how to break down large projects into manageable parts.