VAC Calculator
Variance at Completion analysis with budget forecasting and comprehensive cost management
Use this when
Use this at a regular status date after the scope, schedule, and cost baselines have been approved and progress can be measured objectively.
Prepare
Confirm the status date and bring consistent planned value, earned value, actual cost, and budget-at-completion data from the same reporting period.
Decision supported
Use the signal to decide whether to investigate variance, revise the forecast, protect contingency, or initiate corrective action.
Practitioner guidance and limitations
Interpret and act
Focus on trend and materiality, not a single isolated number. Pair indices and variances with milestone health, risk exposure, and the remaining work.
Professional caution
EVM is only as reliable as the baseline and progress-measurement method. Do not mix data from different cut-off dates or count effort as earned scope.
Common questions about this analysis
What does the VAC Calculator help a project manager decide?
Variance at Completion analysis with budget forecasting and comprehensive cost management Use the result to support a documented decision, action, threshold, or follow-up rather than treating it as a stand-alone score.
How reliable is the VAC Calculator?
Reliability depends on the quality, consistency, and status date of the inputs. Validate source data, record assumptions, and test material results against your approved baseline and expert judgment.
When should the VAC Calculator not be used on its own?
EVM is only as reliable as the baseline and progress-measurement method. Do not mix data from different cut-off dates or count effort as earned scope.
Which inputs require the most attention?
Confirm the status date and bring consistent planned value, earned value, actual cost, and budget-at-completion data from the same reporting period.
What should be shared with stakeholders?
Share the result together with units, status date, source data, assumptions, confidence or range, interpretation, recommended action, owner, and next review date.
Learn the topic: concept, PMP lens, and common mistakes
Core concept
Earned Value Management integrates approved scope, schedule, and actual cost at one status date. Earned value represents budgeted value of completed scope—not effort consumed or invoices paid.
Professional application
Use trends in variance and efficiency indices to identify the cause, update the forecast, and agree corrective action while useful options still remain.
PMP exam and practice lens
Remember the direction of the core measures: positive CV and SV are favorable; CPI and SPI above 1.00 are favorable. Select the EAC or TCPI formula that matches the scenario assumptions.
Common mistakes
- Mixing PV, EV, and AC from different reporting cut-off dates
- Claiming progress without objective completion rules
- Treating an index as the explanation instead of investigating root cause
Before you trust the result
- Confirm one status date and consistent units.
- Retain the input source, owner, and confidence.
- Sense-check the result against an independent benchmark.
- Record the decision, action owner, and review date.
Related practice tools
Budget vs actual comparison
Project completion cost prediction
Budget deviation assessment
Project risk evaluation
Budget and Cost Parameters
Choose the appropriate method for your project management approach
Total authorized budget for the project
Current forecast of total project cost at completion
About VAC Calculation
Variance at Completion (VAC) = Budget at Completion (BAC) - Estimate at Completion (EAC)
Positive VAC indicates under-budget performance, while negative VAC indicates over-budget performance.
What is Variance at Completion (VAC)?
Variance at Completion is the forecasted difference between what you originally budgeted for a project and what you now expect it to actually cost when all the work is done. It is a forward-looking metric that answers the question every sponsor dreads: "Are we going to finish over or under budget, and by how much?" A positive VAC means you expect to finish under budget -- money back in the organization's pocket. A negative VAC means you are heading for a cost overrun that needs to be managed, funded, or both.
VAC is part of the earned value management family of metrics, standing alongside Cost Variance (CV), Cost Performance Index (CPI), and Estimate at Completion (EAC). While CV tells you where you stand right now in terms of cost performance, VAC projects that performance forward to give you a preview of the final outcome. Think of CV as the snapshot and VAC as the forecast. Both are essential, but VAC is what ends up in the steering committee presentation because it speaks to the bottom line at project close.
In the PMBOK Guide, VAC is an output of the Control Costs process. It is calculated using the BAC (your original approved budget) and the EAC (your current forecast of the final cost). The EAC itself can be calculated several ways depending on your assumptions about future performance, which means your VAC is only as reliable as the EAC formula you chose. This is why understanding the relationship between CV, CPI, EAC, and VAC is critical for accurate project financial forecasting.
VAC Formula Explained
BAC (Budget at Completion) is your original, baselined total project budget. This number does not change unless you go through formal change control. EAC (Estimate at Completion) is your best current estimate of what the project will actually cost when finished. The EAC is typically calculated as EAC = BAC / CPI (if current cost efficiency continues) or EAC = AC + (BAC - EV) (if future work returns to planned rates).
The sign convention is straightforward and important. Positive VAC means EAC is less than BAC -- you are forecasted to spend less than budgeted. Negative VAC means EAC exceeds BAC -- you are forecasted to overspend. You can also express VAC as a percentage: VAC% = VAC / BAC x 100. This percentage is useful for comparing budget performance across projects of different sizes.
Step-by-Step Guide to VAC Analysis
Confirm your BAC -- the total approved budget from the cost baseline. This is your reference point and should match the project charter or latest approved budget baseline.
Gather current earned value data: EV (Earned Value), AC (Actual Cost), and CPI (Cost Performance Index). These feed directly into your EAC calculation.
Select the appropriate EAC formula based on your performance assumptions. Use EAC = BAC / CPI if current trends will continue, or EAC = AC + (BAC - EV) if variances are one-time events unlikely to repeat.
Calculate VAC = BAC - EAC. A positive result indicates an expected under-budget finish; a negative result flags a projected overrun requiring corrective action or additional funding.
Communicate the VAC to stakeholders with context -- explain the EAC assumptions, the root causes of variance, and the corrective actions planned. If VAC is significantly negative, initiate change control for budget reallocation or scope adjustment.
Real-World VAC Example
Scenario: Software Platform Migration at 50% Completion
Budget at Completion (BAC): $500,000
Current CPI: 0.89 (running 11% over budget)
Current EV: $225,000
Current AC: $252,809
EAC (CPI-based): $500,000 / 0.89 = $561,798
VAC = $500,000 - $561,798 = -$61,798
VAC% = -$61,798 / $500,000 x 100 = -12.4%
Result: The project is forecasted to overrun by $61,798 (12.4%). Immediate action needed: review remaining scope for cost optimization, negotiate vendor rates, or request budget augmentation through change control.
Common Mistakes to Avoid
- Using the wrong EAC formula -- If your cost overruns are systemic (a CPI consistently below 1.0), use EAC = BAC / CPI. If the overrun was a one-time event, use EAC = AC + (BAC - EV). The formula choice dramatically affects your VAC.
- Ignoring VAC trend -- A single VAC calculation is a snapshot. Track VAC across reporting periods. If VAC is getting more negative each month, the problem is worsening. If it is stabilizing, your corrective actions may be working.
- Confusing VAC with CV -- CV = EV - AC measures current period variance. VAC = BAC - EAC measures projected total variance at the end. They use different inputs and answer different questions.
- Not updating EAC regularly -- VAC is only as good as the EAC behind it. Stale EAC figures produce misleading VAC numbers. Recalculate EAC at every reporting period.
- Reporting VAC without action plans -- A negative VAC without a recovery strategy is just bad news. Always pair variance reporting with concrete corrective actions and timeline commitments.
- Forgetting management reserve -- If VAC is negative but within the management reserve, the project may still be financially covered. Always consider total funding available, not just the cost baseline.
PMP Exam Tips for Variance at Completion
VAC questions on the PMP exam are typically combined with EAC calculation questions. You will often be given BAC and some combination of EV, AC, and CPI, then asked to calculate EAC first and VAC second. Know the formula VAC = BAC - EAC and remember the sign convention: positive is under budget, negative is over budget. The exam may also test VAC as a percentage, so be comfortable with VAC% = VAC / BAC x 100.
The exam loves to test your understanding of the relationship between CV, CPI, EAC, and VAC. Here is the chain: CV tells you the current cost variance; CPI tells you the current cost efficiency; EAC uses CPI (or other inputs) to forecast the total cost; VAC uses EAC to predict the final budget variance. Each metric builds on the previous one. In the PMBOK Guide, all of these appear in the Control Costs process of Project Cost Management. Be prepared for situational questions where you must recommend a specific corrective action based on a negative VAC -- common answers include scope reduction, resource optimization, schedule adjustment, or requesting additional funding through change control.