What Is Cost Growth Index in EVM? Trend Analysis Metric

<div class="ge-article-wrapper"><article class="ge-article-body"><p>The Cost Growth Index tracks how much the forecast final cost (<a href="/en/earned-value/definitions/estimate-at-completion">EAC</a>) has grown relative to the original budget (<a href="/en/earned-value/definitions/budget-at-completion">BAC</a>) over time. While <a href="/en/earned-value/definitions/cost-performance-index">CPI</a> tells you current efficiency, Cost Growth Index tells you whether the damage is getting worse or stabilising.</p><p>This term is part of the <a href="/en/earned-value/definitions">earned value definitions glossary</a>.</p><h2>The Formula</h2><div class="ge-formula-box ge-anim"><span class="ge-formula-label">Formula</span><code>Cost Growth Index = (EAC - BAC) / BAC</code></div><p>A CGI of 0.05 means the forecast has grown 5% beyond the original budget. A CGI of -0.03 means you're forecasting 3% under budget. Track CGI monthly to see whether cost growth is accelerating, stable, or improving.</p><h2>Worked Example</h2><span class="ge-worked-label">Worked Example</span><div class="ge-callout ge-anim"><p><strong>Scenario:</strong> A £25M NEC4 Option C project. Monthly CGI tracking:</p><div class="ge-table-wrap ge-anim"><table class="ge-table"><thead><tr><th>Month</th><th>BAC</th><th>EAC</th><th>CGI</th><th>Trend</th></tr></thead><tbody><tr><td>M3</td><td>£25M</td><td>£25.2M</td><td>0.008</td><td>Minimal</td></tr><tr><td>M6</td><td>£25M</td><td>£25.8M</td><td>0.032</td><td>Growing</td></tr><tr><td>M9</td><td>£25M</td><td>£26.9M</td><td>0.076</td><td>Accelerating</td></tr><tr><td>M12</td><td>£25M</td><td>£27.1M</td><td>0.084</td><td>Stabilising</td></tr></tbody></table></div><p>CGI jumped from 0.032 to 0.076 between months 6 and 9, then slowed. The cost problem hasn't gone away but it's stopped getting worse.</p></div><h2>Common Mistakes</h2><ol><li><strong>Only looking at CGI once.</strong> The value is in the trend, not a single number.</li><li><strong>Not adjusting BAC for CEs.</strong> If BAC doesn't reflect implemented CEs, CGI is inflated.</li></ol><div class="ge-product-note ge-anim"><p><strong>How Gather helps.</strong> Gather tracks cost growth trends automatically from your EVM data. <a href="https://gatherinsights.com/contact">Book a demo</a>.</p></div><h2>Frequently Asked Questions</h2><h3>What CGI triggers concern?</h3><p>Above 0.05 (5% growth) warrants investigation. Above 0.10 needs a formal recovery plan.</p></article></div>