The Cost Performance Index (CPI) is the most honest indicator of the financial health of your projects. It tells you immediately whether your teams are making money or burning through budget – before it’s too late. For agencies that often work with fixed prices or retainers, the CPI is indispensable for securing profitability and detecting "over-servicing" (spending too many hours for the agreed budget) at an early stage.
Definition: What is the Cost Performance Index?
The Cost Performance Index (CPI) is a key metric from Earned Value Management (EVM). It measures the cost efficiency of work performed at a specific point in time. Simply put: it relates the value of what you have already achieved (Earned Value) to what you have spent to achieve it (Actual Cost).
Unlike a simple budget comparison (“We still have 50% of the money left”), the CPI takes into account actual progress in project management. After all, a 50% remaining budget is of no use if only 20% of the work has been completed.
The CPI Formula
The calculation is simple but requires consistent data maintenance:
CPI = Earned Value (EV) / Actual Cost (AC)
- Earned Value (EV): The budgeted value of the work actually completed. (Example: Project budget is £10,000, project is 50% finished → EV = £5,000).
- Actual Cost (AC): The actual costs incurred so far (usually based on time tracking multiplied by internal hourly rates).
How to interpret the result
The CPI value shows you crystal clear where you stand:
- CPI = 1: On target. Costs correspond exactly to the plan.
- CPI > 1 (e.g. 1.2): Excellent! You are working more efficiently than planned (cost savings). For every pound spent, you receive a value of £1.20.
- CPI < 1 (e.g. 0.8): Warning signal! Costs are higher than the value created. You are consuming the budget too quickly. With a CPI of 0.80, you only receive 80 pence in value for every pound spent.
Calculation example from everyday agency life
Imagine your agency is implementing a website relaunch for a fixed price of £20,000. After one month, you take stock:
- Project progress: 25% of tasks are completed (according to the project plan).
Earned Value (EV) = 25% of £20,000 = £5,000 - Actual costs: The team has already invested 60 hours at £100 per hour.
Actual Cost (AC) = £6,000
Calculation: £5,000 / £6,000 = 0.83
Analysis: You are over budget. If you continue working this way, you will likely have £24,000 instead of £20,000 in internal costs by the end of the project (Budget / CPI). Now is the moment to talk to the team: Were there unclear briefings? Was scope creep allowed to happen?
Why the CPI is vital for agencies
In many creative teams, the final reckoning only happens at the end of the project. This is too late for effective steering. The CPI enables active controlling during the project duration:
- Early warning system: Recognise in week 2 that the budget will break in week 10. This is particularly important for retainer budgets, where the monthly margin must be secured.
- Better price negotiations: If you always have a CPI of 0.9 for certain project types (e.g. brand design), you need to adjust your prices or processes.
- Resource allocation: A very high CPI (> 1.2) can mean that you can withdraw senior resources without jeopardising the project goal.
FAQ
What is the difference between CPI and SPI?
While the CPI (Cost Performance Index) measures cost efficiency, the SPI (Schedule Performance Index) looks at the schedule. The SPI answers the question: "Are we faster or slower than planned?". Ideally, you should use both values together for a complete picture.
How often should I calculate the CPI?
For agile teams and agencies, a check aligned with billing cycles or sprints is recommended – roughly every 14 days or monthly. A daily look is usually too granular, while a look once per quarter is too late for corrections.
Can the CPI be negative?
No. Since both Earned Value and Actual Costs are positive monetary amounts, the CPI must always be greater than or equal to 0. However, a value close to 0 indicates a disastrous project.
[.no-toc]Conclusion[.no-toc]
The Cost Performance Index transforms your gut feeling into hard facts. It helps you lead discussions about budgets objectively and protects your agency's margin. To determine the CPI without Excel chaos, you need a clean data basis: planned budgets and precise time tracking are the foundation.
Do you want to keep an eye on your budgets and times with ease? Test awork now for free and make your project controlling run itself.
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