CPI Calculator
Calculate CPI step by step: CPI = EV ÷ AC.
In short
Formula: CPI = EV ÷ AC.
What this calculator does
Calculate CPI step by step: CPI = EV ÷ AC. Worked example, questions and limitations included.
Use it to turn Earned value (EV), Actual cost (AC) into a checked result you can compare, copy, or rerun with different assumptions.
The page shows the formula, a numeric worked example, and the assumptions that affect this earned value calculation.
Inputs and what they mean
- Earned value (EV)
- — number value.
- Actual cost (AC)
- — number value.
How to use it
- Enter each value in the unit shown next to the box (use the unit converter first if your numbers are in other units).
- Check the breakdown to see every intermediate step.
- Read the limitations before relying on the result.
Formula
Definitions follow the PMI PMBOK Guide and the ANSI/EIA-748 earned value management standard.
CPI below 1 means each unit of money spent earns less than one unit of budgeted work.
Actual cost must be above zero, otherwise the index is undefined.
CPI = EV ÷ AC.
Inputs used: Earned value (EV), Actual cost (AC).
Worked example
EV 175,000, AC 190,000
- CPI = 175,000 ÷ 190,000 = 0.921.
Reading the result
The headline figure is the main answer. Any breakdown underneath shows the parts that make it up, so you can check the working and see what changes when you adjust an input.
Limitations and assumptions
- A single cumulative index hides which work is late or over budget.
- Sensitive to how accruals are recorded.
- Unstable early in the project when values are small.
- Results are planning estimates built only from the figures you enter. They are not a guarantee of cost, schedule or delivery, and they do not replace your organisation's own project controls.
- The result depends on the values you enter for this cpi calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.
Common questions
Does CPI recover?
Research on defence projects (Christensen, 1990s) found cumulative CPI rarely improves much after about 20% complete, so treat early overruns seriously. Check the formula, example, and limitations on this page before using the result for a real earned value decision.
How is CPI used for forecasting?
EAC = BAC ÷ CPI assumes current cost efficiency continues. See the EAC calculator for the other documented models.
Is CPI 1.2 a good thing?
Possibly, but a very high CPI can also mean a padded budget or missing actuals. Check the data.
How do I use the CPI Calculator?
Enter the required values for Earned value (EV), Actual cost (AC). The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.
What formula does the CPI Calculator use?
CPI = EV ÷ AC. The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone.
Can the CPI Calculator be used for exact decisions?
Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.
Related tools
Calculate Planned Value step by step: PV = BAC × planned % complete at the status date.
Calculate Earned Value step by step: EV = BAC × actual % complete.
Calculate Actual Cost (Earned Value) step by step: AC = sum of all costs actually incurred for the work performed to the status date.
Calculate Budget At Completion step by step: BAC = sum of the budgets of all work packages in the performance measurement baseline.