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Earned Value Management

Two simple ratios that tell you if your project is on budget and on time. No spreadsheet gymnastics required.

Nahla.AI Team 8 min read Updated February 2026

Why CPI and SPI Matter

Every project generates mountains of data: resource allocations, task durations, cost breakdowns, risk registers, change orders. But when a stakeholder asks "How is the project going?", the answer comes down to two questions:

Are we on budget? That is CPI. Are we on schedule? That is SPI.

CPI (Cost Performance Index) and SPI (Schedule Performance Index) are the two core metrics of Earned Value Management. They compress all the complexity of a project into two numbers that anyone can interpret instantly. A value above 1.0 is good. Below 1.0 is a problem. No ambiguity, no spin.

The power of these two numbers is that they are objective and comparable. You can track them over time to see if things are improving or deteriorating. You can compare them across projects in a portfolio. And you can use them to forecast final cost and completion date with surprising accuracy.

CPI — Cost Performance Index

CPI tells you how efficiently you are converting money into completed work. For every dollar you spend, how much value are you earning?

CPI = EV / AC

Where EV (Earned Value) is the budgeted cost of the work you have actually completed, and AC (Actual Cost) is what you have actually spent.

· CPI > 1.0 — Under budget. You are getting more value than you are spending.

· CPI = 1.0 — On budget. Spending matches earned value exactly.

· CPI < 1.0 — Over budget. You are spending more than the value of completed work.

Example

EV = $100,000 (budgeted cost of completed work) AC = $115,000 (actual cost spent) CPI = $100,000 / $115,000 = 0.87

A CPI of 0.87 means for every $1.00 you spend, you are only earning $0.87 of value. The project is 13% over budget.

CPI is remarkably stable after a project reaches about 20% completion. Research from the US Department of Defense found that CPI rarely improves by more than 10% once a project is 20% complete. If your CPI is 0.85 at the 30% mark, hoping it will magically recover to 1.0 is not a strategy.

SPI — Schedule Performance Index

SPI tells you how efficiently you are using time. Are you completing work at the rate you planned?

SPI = EV / PV

Where EV (Earned Value) is the budgeted cost of work completed, and PV (Planned Value) is the budgeted cost of work that should have been completed by now according to the baseline schedule.

· SPI > 1.0 — Ahead of schedule. You have completed more work than planned.

· SPI = 1.0 — On schedule. Progress matches the baseline plan.

· SPI < 1.0 — Behind schedule. Less work completed than planned.

Example

EV = $180,000 (budgeted cost of completed work) PV = $200,000 (budgeted cost of work planned to date) SPI = $180,000 / $200,000 = 0.90

An SPI of 0.90 means you have completed 90% of the work you planned to have done by now. The project is 10% behind schedule.

One important caveat: SPI converges toward 1.0 as a project nears completion. Even a late project will eventually have an SPI of 1.0 when it finishes (because EV will equal PV at the end). For this reason, many practitioners supplement SPI with SPI(t), the time-based schedule performance index, which does not have this convergence problem. But for most of the project lifecycle, traditional SPI is perfectly useful.

The Performance Quadrant

When you plot CPI and SPI together, you get four quadrants that instantly classify your project health. This is one of the most useful views in earned value management because it shows both dimensions simultaneously.

CPI > 1.0 & SPI > 1.0

Under Budget, Ahead of Schedule

The ideal position. Maintain course and protect the margin.

CPI < 1.0 & SPI > 1.0

Over Budget, Ahead of Schedule

Spending too fast but making progress. Review resource rates and overtime costs.

CPI > 1.0 & SPI < 1.0

Under Budget, Behind Schedule

Saving money but falling behind. May need to increase resources or re-sequence work.

CPI < 1.0 & SPI < 1.0

Over Budget, Behind Schedule

Worst case. Escalate immediately. A recovery plan is needed.

Most projects live in one of the two yellow quadrants. Being in the green quadrant for the entire project duration is rare and often indicates padding in the baseline rather than exceptional performance. What matters most is the trend: are you moving toward green or toward red?

Where Does the Data Come From? New

CPI and SPI are only as reliable as the data behind them. Understanding where each metric gets its inputs helps you interpret the numbers correctly and choose the right data source for your reporting needs.

SPI Is Always From the Schedule

SPI uses Planned Value (PV) and Earned Value (EV), both of which come directly from the schedule S-curve data. This means SPI is consistent regardless of which cost source you select. When you upload a P6 XER file, Nahla extracts the baseline plan and progress data to compute PV and EV at the data date.

CPI Depends on Your Actual Cost Source

CPI uses Actual Cost (AC), and AC can come from two different places. The source you choose will affect your CPI value:

Schedule S-Curve (Default)

AC is derived from the P6 resource cost loading embedded in your schedule file. This reflects the cost data as entered by the planner in Primavera P6. Useful when finance actuals are not yet available or when you want a planner-centric view of cost performance.

CSV Upload (Finance Actuals)

AC comes from a CSV file containing monthly actual cost data provided by your finance or cost control team. This typically reflects invoiced or committed costs and gives a finance-centric view. When a CSV is uploaded, it overrides the schedule-based AC values.

Tip: Use the EVM Source Toggle on the Nahla Dashboard to switch between Schedule S-Curve and CSV actuals. This lets you compare CPI from both perspectives without re-uploading anything.

Why does this matter? The two sources can produce different CPI values for the same project. Schedule-based AC reflects the planner's resource loading, which may lag behind actual expenditure. Finance-based AC reflects real spending, which may include costs not yet captured in the schedule. Neither is wrong — they answer slightly different questions. The best practice is to compare both and investigate any significant gaps.

What to Do When the Numbers Are Bad

Knowing your CPI and SPI is step one. Knowing what to do about it is step two. Here are the standard corrective action paths for each scenario.

When CPI < 1.0 (Over Budget)

• Review cost loading accuracy.Are resource rates up to date? Are all costs being captured? Sometimes a low CPI is a data problem, not a project problem.
• Check resource rates and overtime.Excessive overtime or premium rates can erode CPI quickly. Look at the cost breakdown by resource type.
• Verify scope alignment.Is work being done that was not in the baseline? Uncontrolled scope creep inflates AC without increasing EV.

When SPI < 1.0 (Behind Schedule)

• Analyze the critical path.Delays on critical path activities directly delay the project. Focus recovery efforts here first.
• Check total float and near-critical paths.Activities with low float are at risk of becoming critical. Use float analysis to identify emerging problems.
• Investigate resource conflicts.Are key resources over-allocated? Bottlenecks on shared resources can cascade delays across multiple activities.

When Both CPI < 1.0 and SPI < 1.0

• Escalate immediately.A project that is both over budget and behind schedule is in distress. This requires management attention, not just planner adjustments.
• Develop a formal recovery plan.Define specific actions, responsible parties, and measurable targets. "Try harder" is not a recovery plan.
• Consider re-baselining.If the original baseline is no longer achievable, a formal re-baseline with stakeholder approval may be needed. This resets EVM metrics against a realistic plan.

Ask Nahla AI

You do not need to calculate CPI and SPI manually. Once you upload your schedule to Nahla, you can ask in plain English and get instant answers with full context.

• AI

"What is my CPI?"

Returns the current CPI value with interpretation, trend direction, and the underlying EV and AC values used in the calculation.

• AI

"Show earned value analysis"

Generates the full S-curve chart with PV, EV, and AC plotted over time, plus all EVM metrics including CPI, SPI, EAC, and TCPI.

• AI

"Why is my CPI below 1?"

Analyzes the cost variance drivers and identifies which WBS areas or resource types are contributing most to the overrun.

Every answer links back to the underlying data, so you can drill down from the high-level metric to the specific activities and costs driving it. No black boxes.