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CPI compares earned value with actual cost.
Methodology note. Formulas are based on established Earned Value Management terminology. Core references include Project Management Institute (PMI) educational resources and U.S. Department of Energy EVM guidance. Last reviewed: August 14, 2026. Read methodology · View sources
CPI formula
CPI = EV ÷ ACA CPI of 1.00 indicates earned value equals actual cost. Values below 1.00 indicate unfavorable cost efficiency; values above 1.00 indicate favorable cost efficiency.
Use CPI to forecast EAC
If you expect current cost efficiency to continue, one common forecast is EAC = BAC ÷ CPI. CPI also gives useful context when interpreting TCPI: compare the efficiency achieved so far with the efficiency required on the remaining work.
CPI vs cost variance
Cost variance expresses the difference in currency units, while CPI expresses the same performance relationship as a ratio. Both use EV and AC.