CPI Calculator
Compute Cost Performance Index (CPI) to determine cost efficiency of work performed versus money spent on your project.
CPI = EV / ACInterpretation Guide
- CPI > 1.0Project is under budget.
- CPI = 1.0Project is exactly on budget.
- 0.9 ≤ CPI < 1.0Minor cost overrun — monitor closely.
- CPI < 0.9Significant cost overrun — corrective action needed.
Example
Spent $95,000 (AC) to deliver $80,000 of earned work (EV) → CPI = 0.84. You are spending $1.19 for every $1.00 of value delivered.
Real-world use cases
- Monthly cost performance reviews
- Forecasting Estimate At Completion (EAC)
- Portfolio capital allocation decisions
- Identifying cost-overrun trends early
Common mistakes
- Forgetting to include committed costs in AC.
- Comparing CPI without normalizing for scope changes.
- Ignoring cost variance trends in favor of single-period snapshots.
Professional tips
- Use CPI to forecast EAC: EAC = BAC / CPI.
- Track CPI trend monthly to spot deteriorating performance.
- Combine with SPI for a complete performance picture.
Frequently asked questions
What does a CPI below 1 mean?
Each dollar spent produced less than one dollar of earned value — the project is over budget for the work completed.
Is CPI more important than SPI?
Both matter. CPI is generally a more stable indicator over the project life cycle.
How is CPI used for forecasting?
The most common forecast is EAC = BAC / CPI, assuming current performance continues.
What this tool does
Compute Cost Performance Index (CPI) to determine cost efficiency of work performed versus money spent on your project.
It applies the standard formula CPI = EV / AC so planners, schedulers and PMOs get a defensible number they can put in front of a steering committee.
Looking for the underlying terminology? Open the PM Glossary or the PM Cheat Sheet for quick references on EVM, scheduling and risk terms.
When to use it
- Monthly cost performance reviews
- Forecasting Estimate At Completion (EAC)
- Portfolio capital allocation decisions
- Identifying cost-overrun trends early
Typical owners: project managers, planning engineers, project controls leads and PMO analysts running weekly or monthly performance reviews on EPC, infrastructure, IT and construction projects.
How to interpret the result
Treat the number as a signal, not a verdict. Read it together with the trend over the last 3–6 reporting periods, the critical-path status, and the risk register before you change the plan.
- Compare against the baseline, not against another project.
- Investigate the drivers behind the value before reporting it up.
- Pair it with at least one complementary KPI (cost, schedule, risk or quality).
Worked example
Spent $95,000 (AC) to deliver $80,000 of earned work (EV) → CPI = 0.84. You are spending $1.19 for every $1.00 of value delivered.
In a real project review, document the inputs, the resulting value, the interpretation, and the corrective action you committed to. That audit trail is what turns a calculator output into a controls decision.
In-depth guide: CPI Calculator
Cost Performance Index (CPI) is the EVM ratio that answers the question every sponsor asks: 'For every dollar we spent, how many dollars of work did we get back?'. A CPI of 0.85 means we are getting 85 cents of value per dollar spent, and — unless something changes — we will finish roughly 18% over budget. AACE International's recommended practice 80R-13 calls CPI the most reliable EVM metric because it stabilises faster than SPI and remains valid right through to project close-out.
Empirically, on large defence and EPC programmes the cumulative CPI tends to stabilise within ±0.05 by the 20% completion mark and rarely improves materially after that point. This is the basis of the standard EAC formula EAC = BAC / CPI: the assumption that the cost performance you have today is the cost performance you will get for the rest of the project. That assumption is conservative on well-run projects and optimistic on troubled ones, but it is rarely off by more than 10%.
On the ground, CPI is computed by the project controls or cost engineering team from the cost ledger (AC) and the earned-value report (EV) at the end of every accounting period. The trick is making sure AC and EV are measured on the same scope and same period cut-off — a mismatch of even one week can swing CPI by several percentage points.
When to use it (and when not to)
Use CPI for monthly cost reviews, EAC forecasting, change-control board submissions, and capital-allocation decisions at the portfolio level. It is also the right number for contract-incentive calculations on cost-reimbursable and cost-plus-incentive-fee contracts.
Do not use CPI in isolation when the project has large committed-but-not-yet-invoiced costs (long-lead equipment, framework subcontracts). In that case, normalise AC to include commitments, or supplement CPI with a commitment-adjusted variant (CPI* = EV / (AC + Open Commitments)).
Related KPIs to read alongside
Read CPI together with SPI (schedule efficiency), CV (cost variance in dollars), EAC and VAC (forecast outcome), and TCPI (required future efficiency to hit budget). For contract management, also compute the Cost-Schedule Index (CPI × SPI) as a single combined health metric — values below 0.85 typically warrant escalation.
Worked example — software platform build
An enterprise software build has a BAC of $4.8M over 18 months. At month 9, the cost ledger shows $2.7M of actual cost. The product owner certifies that 50% of the planned scope is complete, so EV = $2.4M.
CPI = 2.4 / 2.7 = 0.889. Below 0.9 but above 0.85 — the cost overrun is real but not catastrophic. Plugging into the standard formula: EAC = BAC / CPI = 4.8 / 0.889 = $5.40M, a forecast overrun of $600k against a $4.8M baseline (12.5%).
The team runs a sensitivity: if CPI continues at 0.889 the overrun is $600k; if they can lift to 0.95 for the rest of the project the overrun shrinks to $290k; if it drops to 0.80 the overrun grows to $1.2M. They take the $290k recovery target to the change board with a concrete plan — replace two contractors with internal staff, defer two low-value features to phase 2 — and get approval to draw $300k from the management reserve as a contingency.
Decision table
| Signal | What it means | Recommended action |
|---|---|---|
| CPI ≥ 1.00 | Under budget — getting more value per dollar than planned. | Verify EV is not over-claimed; consider releasing contingency. |
| 0.95 ≤ CPI < 1.00 | Minor overrun within normal variance. | Monitor; no action required unless trend is negative. |
| 0.90 ≤ CPI < 0.95 | Material cost inefficiency. | Drill into top-5 cost accounts; revisit EAC. |
| CPI < 0.90 | Significant overrun, EAC at risk. | Trigger formal change control; assess scope reduction or additional funding. |
Common pitfalls in the field
- Excluding commitments from AC is the most common error. A project that has placed a $1.2M PO for switchgear but not yet invoiced will look fine on CPI right up until the invoice lands. Always reconcile AC against the commitment register at month-end.
- Comparing CPI across projects of different scope or contract type. A lump-sum civil project and a time-and-materials software project will produce CPIs that are not directly comparable. Use CPI for trend within a project; use unit-rate metrics (cost per m³, cost per story point) for cross-project benchmarking.
- Forgetting that CPI is a lagging indicator. By the time CPI drops below 0.9, the overrun has already been spent. Leading indicators — productivity rate, rework hours, change-request volume — give you 30–60 days of advance warning that CPI will deteriorate.
Featured in Academy articles
This calculator is referenced in the FAQs of these Academy articles — read them to understand the theory behind the numbers.
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