Schedule Cost Index (SCI) in EVM Explained

<div class="ge-article-wrapper"><nav class="ge-toc" aria-label="Table of contents"><p class="ge-toc-label">In this article</p><ul class="ge-toc-list"><li><a href="#the-formula">The Formula</a></li><li><a href="#the-quadrant-diagram">The Quadrant Diagram</a></li><li><a href="#worked-example-42m-highway-improvement">Worked Example: £42M Highway Improvement</a></li><li><a href="#why-sci-works-better-than-separate-metrics">Why SCI Works Better Than Separate Metrics</a></li><li><a href="#sci-threshold-guide">SCI Threshold Guide</a></li><li><a href="#common-mistakes">Common Mistakes</a></li><li><a href="#frequently-asked-questions">Frequently Asked Questions</a></li></ul></nav><article class="ge-article-body"><p>The Schedule Cost Index, SCI for short, combines <a href="/en/earned-value/definitions/cost-performance-index">CPI</a> and <a href="/en/earned-value/definitions/schedule-performance-index">SPI</a> into one composite metric. The formula is CPI multiplied by SPI. That's it. One number that tells you how the project is performing across both dimensions simultaneously.</p><p>Why bother? Because reporting CPI and SPI separately sometimes lets people focus on whichever one looks better. "Yes, we're over budget, but we're ahead of programme." Or: "We're behind programme, but look at the cost efficiency." SCI doesn't let you hide. A project needs to be healthy on both axes to score well.</p><p>SCI is part of the <a href="/en/earned-value/definitions">earned value definitions glossary</a>. For the individual components, see the <a href="/en/earned-value/cpi-spi">CPI and SPI formula page</a>.</p><h2 id="the-formula">The Formula</h2><div class="ge-formula-box ge-anim"><span class="ge-formula-label">Formula</span><code>SCI = CPI x SPI</code></div><p>Where:</p><ul><li><strong><a href="/en/earned-value/definitions/cost-performance-index">CPI</a></strong> = EV / AC (cost efficiency)</li><li><strong><a href="/en/earned-value/definitions/schedule-performance-index">SPI</a></strong> = EV / PV (schedule efficiency)</li></ul><p>An SCI of 1.0 means the project is perfectly on budget and on programme. Above 1.0, it's doing well on both. Below 1.0, at least one dimension, and usually both, is underperforming.</p><p>The multiplication is what makes it unforgiving. A CPI of 0.95 and SPI of 0.95 look manageable individually. Multiply them and you get an SCI of 0.9025. Two minor problems compound into a bigger one.</p><h2 id="the-quadrant-diagram">The Quadrant Diagram</h2><pre class="ge-ascii-diagram ge-anim"> SPI | 1.2 | Under budget Under budget | Behind schedule Ahead of schedule | | SCI ≈ 0.96-1.08 SCI &gt; 1.0 | (best quadrant) 1.0 |─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ | | Over budget Over budget | Behind schedule Ahead of schedule | | SCI &lt; 0.85 SCI ≈ 0.85-1.0 0.8 | (worst quadrant) | +────────────────────────────────────── CPI 0.8 1.0 1.2 ──── SCI = 1.0 contour (curves from top-left to bottom-right) ─ ─ SCI = 0.8 contour (further out – danger zone) Contour lines: CPI × SPI = constant Any point ON the SCI = 1.0 curve means project is composite-neutral Any point INSIDE the curve (toward origin) = underperforming</pre><p>The quadrant makes it obvious. Bottom-left is the danger zone, over budget and behind programme. Top-right is where you want to be. The SCI contour lines curve through the chart; every point on the SCI = 1.0 line represents a different mix of CPI and SPI that multiplies to 1.0 (e.g., CPI 0.95 x SPI 1.053, or CPI 1.10 x SPI 0.909).</p><h2 id="worked-example-42m-highway-improvement">Worked Example: £42M Highway Improvement</h2><span class="ge-worked-label">Worked Example</span><div class="ge-callout ge-anim"><p><strong>Scenario:</strong> A £42M NEC4 Option C highway improvement programme, 30 months duration. At the month 14 review (July 2025), the earned value analysis shows:</p><ul><li><strong><a href="/en/earned-value/definitions/planned-value">PV</a></strong> = £22.4M</li><li><strong><a href="/en/earned-value/definitions/earned-value">EV</a></strong> = £19.7M</li><li><strong><a href="/en/earned-value/definitions/actual-cost">AC</a></strong> = £21.6M</li></ul><p><strong>CPI</strong> = £19.7M / £21.6M = <strong>0.912</strong><strong>SPI</strong> = £19.7M / £22.4M = <strong>0.880</strong><strong>SCI</strong> = 0.912 x 0.880 = <strong>0.803</strong></p><p>Individually, a CPI of 0.91 might prompt concern but not panic. An SPI of 0.88 is clearly behind but "manageable." But SCI of 0.80 paints the real picture: the project is simultaneously leaking money and losing time. That combination is worse than either problem alone because schedule recovery typically costs money (acceleration, overtime, additional resources), which makes the CPI worse, which makes the SCI worse. It's a spiral.</p><p>The <a href="/en/earned-value/eac-etc-tcpi">EAC</a> using CPI alone: £42M / 0.912 = £46.1M. The EAC using CPI x SPI: £42M / 0.803 = £52.3M.</p><p>That's a £6.2M difference in forecast outturn. The combined formula produces the more pessimistic, and often more realistic, forecast. On this job, the final account came in at £50.8M. The SCI-based forecast was closer to reality.</p></div><h2 id="why-sci-works-better-than-separate-metrics">Why SCI Works Better Than Separate Metrics</h2><p>I've sat in enough project board meetings to know what happens when you present CPI and SPI as separate numbers. The project director picks the better one. "We're 0.91 on cost. That's not terrible." And SPI of 0.88? "We've got a recovery plan." Nobody multiplies them together because the result is uncomfortable.</p><p>SCI forces the uncomfortable conversation. It's harder to dismiss 0.80 than it is to dismiss two numbers in the low 0.90s.</p><p>There's a second reason SCI is useful: trending. Plotting SCI over time on a run chart gives you one line to watch instead of two. If SCI is trending down, the project is deteriorating, even if one component is improving while the other worsens. That single trend line simplifies reporting for senior management who don't have time to unpack CPI and SPI individually every month.</p><h2 id="sci-threshold-guide">SCI Threshold Guide</h2><div class="ge-table-wrap ge-anim"><table class="ge-table"><thead><tr><th>SCI Range</th><th>Project Health</th><th>Typical Response</th></tr></thead><tbody><tr><td><strong>> 1.0</strong></td><td>Healthy, performing well on both axes</td><td>Continue monitoring. Don't get complacent.</td></tr><tr><td><strong>0.90 to 1.0</strong></td><td>Minor concerns, one or both axes slightly off</td><td>Root cause analysis. Targeted corrective actions.</td></tr><tr><td><strong>0.80 to 0.89</strong></td><td>Significant issues, compounding cost and schedule problems</td><td>Formal recovery plan. Update <a href="/en/earned-value/eac-etc-tcpi">EAC</a>. Escalate to project director.</td></tr><tr><td><strong>0.70 to 0.79</strong></td><td>Severe, project is in distress on both dimensions</td><td>Major intervention. Consider scope, programme, or target adjustments.</td></tr><tr><td><strong>< 0.70</strong></td><td>Critical, recovery to plan is unlikely</td><td>Re-baseline or terminate. The original plan is no longer achievable.</td></tr></tbody></table></div><h2 id="common-mistakes">Common Mistakes</h2><p><strong>1. Using SCI as a replacement for CPI and SPI.</strong> It's a supplement, not a substitute. SCI of 0.90 could mean CPI 0.95 x SPI 0.947 (mild across both) or CPI 1.06 x SPI 0.849 (ahead on cost but severely behind on time). Same SCI, completely different management actions. Always report all three.</p><p><strong>2. Ignoring the convergence problem.</strong> Because SCI includes SPI, it inherits <a href="/en/earned-value/definitions/schedule-performance-index">SPI's convergence flaw</a>, SPI trends toward 1.0 at project end regardless of actual delays. In the final third of a project, consider using SPI(t) instead of traditional SPI when calculating SCI.</p><p><strong>3. Setting thresholds too loosely.</strong> Some organisations set an SCI warning threshold at 0.80. That's too late. By the time SCI hits 0.80, you've likely been deteriorating for months. Set the amber threshold at 0.90 and red at 0.80.</p><div class="ge-product-note ge-anim"><p><strong>How Gather helps.</strong> Gather's AI reads your site diaries daily and maps progress against your cost-loaded programme, giving you accurate earned value data without manual spreadsheet updates. <a href="https://gatherinsights.com/contact">Book a demo</a> to see it working on a live NEC4 project.</p></div><h2 id="frequently-asked-questions">Frequently Asked Questions</h2><h3>What is a good SCI for a construction project?</h3><p>Above 0.90 is manageable. Above 0.95 is healthy. Consistently above 1.0 is excellent. In practice, I've rarely seen a UK construction project maintain SCI above 1.0 for more than six consecutive months, construction is inherently messy and one or both axes will dip eventually.</p><h3>How is SCI different from just averaging CPI and SPI?</h3><p>Multiplication is harsher than averaging. CPI 0.90 and SPI 0.85 average to 0.875, which doesn't sound terrible. But SCI = 0.765, which sounds exactly as bad as it is. The multiplication punishes combined underperformance more than an average would, which is appropriate because cost and schedule problems compound each other in practice.</p><h3>Can SCI be negative?</h3><p>No. Both CPI and SPI are ratios that can't be negative (you can't have negative earned value or negative actual cost in any meaningful sense). SCI will always be a positive number, though it can be very small on severely distressed projects.</p><h3>When should I use SCI instead of individual metrics?</h3><p>SCI is most useful for portfolio-level reporting, when you're tracking 5, 10, or 20 projects and need a single health indicator for each. At the individual project level, you'll still want CPI and SPI separately to diagnose what's actually going wrong. Think of SCI as the headline; CPI and SPI as the detail.</p></article></div>