There are roughly a dozen formulas in the earned value management formula set. Most EVM training presents them in a tidy sequence — PV, EV, AC, then the variance formulas, then the indices, then the forecasting formulas — as if they’re all equally important and you should track all of them on every project. I’ve come to think that’s the wrong framing. Three or four of these formulas drive almost every meaningful decision in project cost management. The rest exist in training materials and reporting templates without anyone acting on them. This article is organized around that reality: which earned value management formula actually matters, which ones I use on every project, and which ones I report because the template requires them but rarely find useful.
Table of Contents
The Three Earned Value Management Numbers Everything Depends On
Before any formula, three baseline metrics. They’re worth being precise about because the most common EVM errors — systematically optimistic CPI, misleading SPI, wrong EAC — usually trace back to fuzzy definitions of one of these three inputs.
Planned Value (PV): the budgeted cost of work scheduled to be complete by the status date. Not the total budget. The slice the baseline schedule says should be done right now. PV at project completion equals BAC (Budget at Completion).
Earned Value (EV): the budgeted cost of work actually completed. Not what it cost — what it was budgeted to cost. This is the number that makes earned value analysis different from simple cost tracking. Without it, you can’t separate cost performance from schedule performance, which means you can’t tell the difference between “we’re underspent because work is efficient” and “we’re underspent because we’ve barely done anything.”
Actual Cost (AC): what you’ve actually spent. Nothing more. AC alone is just a spending figure — it tells you nothing about whether the work was delivered.
One note on EV that belongs here rather than at the end as a caveat: EV is only as good as the percent-complete figure feeding it. On one project I worked on — infrastructure, about fourteen months in — CPI had been running at 1.08 for three reporting periods and the team was using it to argue the project was tracking well. When we went back through the work package progress claims, about a third of them had been consistently overclaimed. By 10-15 percentage points each. The CPI was right by the math. The inputs were wrong. The actual position was closer to 0.89. By the time we had accurate data, the recovery window was much smaller than it should have been. I think about that project whenever I see a suspiciously stable CPI.
Cost Graph
Let’s assume that we are managing a highway project and the project is 5 months along. Below graph shows budgeted cost versus actual cost situation.
This graph shows that our planned value (budgeted cost) is significantly more than actual costs and we appear to be underspending. But what can we say about the project’s performance? what about the actual work completed? Are we behind or above the schedule? Is it possible to finish this highway project on time? Unfortunately, this graph itself does not include sufficient information to answer these questions. We need more parameters for decision making.
Cost and Earned Value Graph
Let’s review the graph below for a better understanding of the concept.
In order to see our projects real performance, we are adding the earned value parameter to this graph.
When we add the value of work performed to the graph we see that our actual schedule is not in a good situation. The earned value as of the 5th Month is significantly less than the budgeted cost so we are behind schedule.
And the earned value as of the 5′ th Month is less than the actual cost so we are over budget.The project looked healthy on the first graph. It isn’t. That’s exactly why the earned value management formula set exists — to make this invisible problem visible.
The CPI Formula — the One That Actually Drives Decisions
Cost Performance Index measures cost efficiency per unit of work delivered. It’s the earned value management formula I look at first on any project and the one I’d keep if I could only keep one.
CPI of 1.0: one dollar of work per dollar spent — exactly as planned. CPI of 0.84: 84 cents of work per dollar, meaning about 19% over budget on work delivered. CPI of 1.15: 15% under budget relative to completed work.
The reason CPI matters more than the variance formulas is that it’s scale-independent — you can compare CPI across tasks, phases, projects, and time periods without adjusting for project size. Cost Variance (CV = EV − AC) tells you the dollar gap but doesn’t tell you whether that gap is large or small relative to the work involved. CPI does.
The finding I find most important in all of EVM: CPI tends to stabilize after a project reaches roughly 20% completion. A reading established in the first few months is a strong predictor of final cost performance — much stronger than most project managers treat it. Teams see CPI of 0.79 at month three and wait for it to improve. Often it doesn’t. By month eight it’s still 0.79 and everyone is surprised. The practical implication: when CPI is bad early, act on it early. The room to course-correct shrinks as the project matures. By the final third of a project, the formulas mostly tell you how far over budget you’ll finish, not how to avoid it.
Cost Variance exists and belongs in reporting:
Positive means under budget for completed work. Negative means over. I include it in every status report because sponsors often find dollar figures more intuitive than indices. But the decision-making happens off CPI, not CV.
Earned Value Management Formulas I Barely Use Anymore
This section covers SV and SPI. They’re in every EVM guide and every reporting template. I report them because the template requires it. I’ve largely stopped using them for actual decisions. Neither earned value management formula gives reliable information in the project phase where decisions matter most — late execution.
Schedule Variance:
Schedule Performance Index:
The reason I’ve pulled back: both formulas are mathematically forced toward zero (SV) and 1.0 (SPI) at project completion, because eventually all planned work gets done — EV catches up to PV regardless of how late the project finishes. A project that’s four months overdue will show improving SPI in its final reporting periods. That’s not recovery. That’s the denominator catching up to the numerator as the project nears completion. After roughly 70% complete, SPI is actively misleading as a schedule indicator.
For late-phase schedule assessment — which is when you actually most need to know whether you’re on track — tracking actual milestone dates against the baseline schedule is more reliable than watching SPI improve itself into false reassurance.
Early in a project, SPI is worth watching. By the second half, I mostly ignore it and look at milestones instead.
The EAC Formula Problem: Three Versions, and Why the Choice Matters
Estimate at Completion forecasts total project cost. There are three EAC formulas, and the difference between them is not mathematical — it’s an assumption about what will happen for the rest of the project. Most teams apply the standard formula without stating that assumption explicitly, which is where EAC forecasts go wrong.
Standard EAC formula — assumes current CPI continues:
This is the right formula when there’s no specific reason to believe cost efficiency will change. If CPI has been 0.84 for four months, this formula assumes it stays at 0.84 for the remaining work. Given the stabilization evidence, this is usually the most defensible forecast once a project is past 20% complete. It’s also the formula teams reach for automatically — not because they’ve decided current CPI will continue, but because it’s the default and it takes the least effort to justify.
Optimistic EAC — overrun was a one-time event:
This says: whatever caused the overrun so far won’t repeat, and the remaining work will cost exactly as originally planned. It’s appropriate when you can name a specific, non-recurring cause for the overrun — a specific procurement failure that’s been resolved, a weather event that affected a bounded phase, a subcontractor who’s been replaced. “We expect to do better going forward” is not that cause. I’ve seen this formula used to produce a more comfortable EAC without the supporting argument, which makes it a tool for wishful forecasting rather than honest forecasting.
Pessimistic EAC — cost and schedule pressure compound:
This compounds cost inefficiency and schedule pressure together. The right formula when being behind schedule is itself generating costs — extended overhead, premium rates to catch up, contractual penalties. I’m honestly not sure I use this one enough. It usually produces the number nobody wants to see in a sponsor meeting, which creates an incentive to reach for the standard formula instead. On projects where schedule pressure is actively compounding cost overruns, the pessimistic formula is often the most honest.
ETC and VAC follow from whichever EAC you choose:
ETC is the remaining cash needed to finish. VAC is the projected overrun or underrun. Negative VAC is what you bring to a sponsor when discussing additional project cost management or additional funding. Present it as a projection based on a stated assumption — which version of the earned value management formula you used and why — rather than as a certainty.
TCPI: The Earned Value Management Formula Nobody Runs
To Complete Performance Index asks the question most project teams never ask directly: given where we are, what cost efficiency must the remaining work achieve to hit a specific budget target?
The result is a required CPI for the remaining work. Compare it to your current CPI and you have an immediate plausibility test for your budget target.
If current CPI is 0.84 and TCPI to meet the original budget is 1.29, that means the remaining work needs to run at 54% better cost efficiency than established performance. That’s not impossible — if there’s a specific reason to believe efficiency will improve significantly — but it needs to be named and justified. What usually happens instead: the project keeps reporting against the original budget, TCPI sits at 1.29, nobody calculates it, and the forecast overrun surfaces late when there’s less room to respond.
There’s a second version for testing whether a revised EAC is internally consistent:
If you’ve set EAC using the standard formula (BAC ÷ CPI), then TCPI vs EAC should return your current CPI exactly. If the numbers don’t match, there’s an error in the calculation. It’s a quick consistency check I run every time I produce a new EAC.
I find TCPI most useful in conversations where a project is visibly struggling but still being measured against the original budget. The number makes the recovery requirement explicit — not as an opinion but as arithmetic. That changes the nature of the conversation.
Full Calculation on a Struggling Project
A pipeline rehabilitation project. Numbers modified for confidentiality but the performance pattern is real — CPI established early and stable, schedule pressure compounding the cost problem.
BAC: $8,370,000. Planned duration: 16 months. Status at month 10.
PV = $5,231,250
EV = $4,603,500
AC = $5,480,000
CV = $4,603,500 − $5,480,000 = −$876,500. The completed work cost $876K more than budgeted.
CPI = 4,603,500 ÷ 5,480,000 = 0.840.
SPI = 4,603,500 ÷ 5,231,250 = 0.880. (Month 10 of 16 — still early enough that SPI is worth noting.)
Standard EAC:
Pessimistic EAC (with schedule pressure compounding):
ETC = $9,964,286 − $5,480,000 = $4,484,286 still needed at current efficiency.
VAC = $8,370,000 − $9,964,286 = −$1,594,286 projected overrun.
Now TCPI against the original budget:
Required CPI of 1.303 against established CPI of 0.840. The remaining work would need to run at 55% better cost efficiency than the project has managed so far. On this project there was no structural change that would explain that kind of improvement — no major scope reduction, no significant team change, no procurement shift. The original budget of $8.37M was no longer a realistic target and the honest conversation was about the $9.96M forecast, not about how to close a 55% efficiency gap.
TCPI vs standard EAC as consistency check: $3,766,500 ÷ $4,484,286 = 0.840. Matches CPI exactly — the calculation is consistent.
For teams using Primavera P6 or similar tools, most of these calculations can be automated and tracked as trends across reporting periods. The trend matters more than any single period reading — a CPI declining from 0.91 to 0.84 over three months tells a different story than one that’s been stable at 0.84 since month four. See our detailed earned value management example for a worked project from initiation to close.
For additional context on EVM in government and major program contexts, the DoD EVM Implementation Guide and the APM’s EVM handbook cover the cost control requirements and reporting standards in detail. The formulas are the same; the governance around them differs considerably by sector.
I am a Civil Engineer in HES Consultancy Limited, experience as Director and Resident of Works and Technical, Financial and Administrative Project Audit. I have skills in the area of Procurement, Tenders and Contracting. I am PMP and PRINCE2 Certified. Monitoring and Control with the Earned Value Method.
