What Is ETC? Estimate to Complete Formula for Construction

<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="#how-etc-works">How ETC Works</a></li><li><a href="#why-finance-directors-care-about-etc-more-than-eac">Why Finance Directors Care About ETC More Than EAC</a></li><li><a href="#worked-example-12m-budget-ac-of-4-2m-eac-of-13-2m">Worked Example: £12M Budget, AC of £4.2M, EAC of £13.2M</a></li><li><a href="#formula-based-vs-bottom-up-etc">Formula-Based vs Bottom-Up ETC</a></li><li><a href="#etc-trend-analysis">ETC Trend Analysis</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>Estimate to Complete (ETC) tells you how much more money you need to spend to finish the project. Not the total cost. Not what you've already spent. Just the forward-looking number: what's left. The formula is simple. The conversations it triggers are anything but.</p><p><strong>ETC = <a href="/en/earned-value/definitions/estimate-at-completion">EAC</a> - <a href="/en/earned-value/definitions/actual-cost">AC</a></strong></p><p>That's it. But don't let the simplicity fool you. In the right room, ETC matters more than any other <a href="/en/earned-value">earned value</a> metric. ETC is part of the <a href="/en/earned-value/definitions">earned value definitions glossary</a>. For the full forecasting picture, see the <a href="/en/earned-value/eac-etc-tcpi">EAC, ETC and TCPI page</a>.</p><h2 id="how-etc-works">How ETC Works</h2><p>ETC strips out sunk costs and isolates the remaining funding requirement. Picture it like this:</p><pre class="ge-ascii-diagram ge-anim"> PROJECT COST TIMELINE ====================== Day 1 Today Completion | | | | Already Spent | Still to Spend | | (Actual Cost) | (Estimate to Complete) | |=================================&gt;|===========================&gt;| | AC = £4.2M | ETC = £9.0M | | | | |&lt;===============================================================&gt;| | EAC = £13.2M | | (Total Forecast) | | | |&lt;============================================&gt;| | BAC = £12.0M | | (Original Budget) | | | |&lt;==========| | OVERRUN | | £1.2M | |===========| </pre><p>The diagram makes the relationships clear. BAC is what you planned to spend. EAC is what you'll actually spend. AC is what you've already spent. And ETC is the gap between where you are now and where you're going to end up.</p><h2 id="why-finance-directors-care-about-etc-more-than-eac">Why Finance Directors Care About ETC More Than EAC</h2><p>Here's something I learned early in my career, the hard way. Project managers obsess over EAC because it tells them the total outturn. But the finance director? She doesn't care about the total. She already knows the project is going to overrun.</p><p>What she needs to know is: "How much more cash do I need to allocate from the group's portfolio?"</p><p>That's ETC.</p><p>On a Tier 1 contractor running 30+ live projects, the group FD is managing cash flow across all of them. When you tell her EAC is £32M, she has to do mental arithmetic to work out how much is left. When you tell her ETC is £14.5M, she can plug that straight into the cash flow model. No maths required.</p><p>I've sat in monthly reviews where the project team fixates on CPI (it's at 0.93, they say, manageable) while the FD watches ETC climb by £200K every month. Same data. Completely different concern.</p><h2 id="worked-example-12m-budget-ac-of-4-2m-eac-of-13-2m">Worked Example: £12M Budget, AC of £4.2M, EAC of £13.2M</h2><span class="ge-worked-label">Worked Example</span><div class="ge-callout ge-anim"><p><strong>Scenario:</strong> A £12M NEC4 Option C earthworks package on a highways scheme. Month 7 of 14. During month 5, the team hit unexpected contaminated ground that wasn't in the site investigation report. CPI dropped to 0.88 and hasn't recovered. The commercial team runs the numbers.</p><p><strong>Given:</strong></p><ul><li><a href="/en/earned-value/definitions/budget-at-completion">BAC</a> = £12,000,000</li><li><a href="/en/earned-value/definitions/earned-value">EV</a> = £4,800,000 (40% earned)</li><li>AC = £5,455,000</li><li><a href="/en/earned-value/definitions/cost-performance-index">CPI</a> = 0.88</li></ul><p>The contamination fundamentally changed the remaining scope, so the team uses a bottom-up re-estimate rather than the CPI formula:</p><ul><li>AC to date = £4,200,000 (costs committed at the cut-off for the ETC exercise, excluding £1.255M of accruals still processing)</li><li>Bottom-up ETC (package managers re-estimate remaining earthworks, remediation, and disposal) = £9,000,000</li><li><strong>EAC = AC + Bottom-up ETC = £4,200,000 + £9,000,000 = £13,200,000</strong></li></ul><p><strong>ETC = EAC - AC = £13,200,000 - £4,200,000 = £9,000,000</strong></p><p>The original remaining budget was BAC - AC = £12,000,000 - £4,200,000 = £7,800,000.</p><p>So ETC exceeds the remaining budget by £1,200,000. That's the additional funding the finance team needs to find.</p><p><strong>The conversation this triggers:</strong></p><div class="ge-table-wrap ge-anim"><table class="ge-table"><thead><tr><th>Question</th><th>Answer</th></tr></thead><tbody><tr><td>How much have we spent?</td><td>£4.2M (AC)</td></tr><tr><td>How much more do we need?</td><td>£9.0M (ETC)</td></tr><tr><td>How much more than budget?</td><td>£1.2M above remaining budget</td></tr><tr><td>What's driving the increase?</td><td>Ground contamination remediation: £1.4M not in original estimate, partially offset by £200K savings elsewhere</td></tr><tr><td>When do we need the cash?</td><td>£3.2M in months 8 to 10 (remediation), £5.8M in months 11 to 14 (remaining earthworks)</td></tr></tbody></table></div><p>That last row is where ETC becomes genuinely useful. It's not just a number. It's a cash flow conversation.</p></div><h2 id="formula-based-vs-bottom-up-etc">Formula-Based vs Bottom-Up ETC</h2><p>There are two fundamentally different approaches and they serve different purposes.</p><p><strong>Formula-based ETC</strong> is calculated as EAC minus AC. It inherits all the assumptions of whichever EAC formula you used. Quick, consistent, and perfectly adequate when the project is running to a predictable pattern.</p><p><strong>Bottom-up ETC</strong> ignores formulas entirely. You go back to the package managers, ask them to re-estimate every remaining activity, and sum it up. Slower. More expensive. But when something fundamental has changed, it's the only honest approach.</p><div class="ge-table-wrap ge-anim"><table class="ge-table"><thead><tr><th>Approach</th><th>Speed</th><th>When to Use</th><th>Reliability</th></tr></thead><tbody><tr><td>Formula-based (EAC - AC)</td><td>Minutes</td><td>Stable CPI, no fundamental changes</td><td>High if CPI is stable for 3+ months</td></tr><tr><td>Bottom-up re-estimate</td><td>Days to weeks</td><td>Major scope change, re-baseline, tender assumptions clearly wrong</td><td>High if package managers are honest</td></tr></tbody></table></div><p>On complex infrastructure jobs, I calculate both and compare. If they're within 5% of each other, confidence is high. If they diverge by 15% or more, something in the assumptions is wrong and it needs investigating before the next board report.</p><h2 id="etc-trend-analysis">ETC Trend Analysis</h2><p>A single ETC number tells you what's left. The trend tells you whether things are getting better or worse.</p><p>Plot ETC monthly. On a healthy project, ETC declines proportionally to progress. Earn 10% more work, ETC drops by roughly 10%. Simple.</p><p>But if ETC is flat or rising even as you complete more work, costs are growing faster than progress. That's an early warning signal, often earlier than <a href="/en/earned-value/definitions/cost-performance-index">CPI</a> alone would flag, because CPI is a cumulative measure and slow to react. ETC trend catches the shift in real time.</p><h2 id="common-mistakes">Common Mistakes</h2><p><strong>Confusing ETC with remaining budget.</strong> Remaining budget is BAC minus AC. ETC is EAC minus AC. They're only the same if the project is running exactly to plan (CPI = 1.0). On any project with a CPI below 1.0, ETC will be higher than remaining budget. The gap is the forecast overrun.</p><p><strong>Not updating ETC when EAC changes.</strong> Sounds obvious. But I've reviewed project reports where EAC was revised upward and ETC wasn't recalculated. The board is making cash flow decisions on stale numbers.</p><p><strong>Presenting ETC without a spending profile.</strong> A single ETC number is useful. An ETC broken down by month across the remaining programme is transformative. The FD doesn't just need to know you need £9M more. She needs to know you need £3.2M in the next three months and £5.8M after that.</p><p><strong>Using formula-based ETC after a fundamental change.</strong> If you've just implemented a major compensation event that restructured half the remaining work, your CPI-based EAC is measuring a project that no longer exists. Go bottom-up.</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's the difference between ETC and remaining budget?</h3><p>Remaining budget is BAC minus AC: the money left in the original approved budget. ETC is EAC minus AC: the money you'll actually need based on current performance or re-estimate. If CPI is below 1.0, ETC will be higher than remaining budget. The gap between them is the projected additional funding requirement.</p><h3>Can ETC be negative?</h3><p>Not meaningfully. A negative ETC would mean EAC is less than AC, implying the project will cost less than what you've already spent. In practice, this doesn't happen. If your formula produces a negative ETC, check your inputs: either AC is overstated, EAC is wrong, or costs have been misallocated.</p><h3>How does ETC feed into cash flow forecasting?</h3><p>ETC is the starting point. If ETC is £9M spread across 7 remaining months, the finance team profiles that spend against the remaining programme. Early months might be heavier (if the expensive work is next) or lighter (if the big costs are at the end). Without ETC, cash flow forecasts are based on the original budget, which may bear no resemblance to what's actually needed.</p><h3>Should I report ETC or EAC to the board?</h3><p>Both. But lead with ETC when talking to finance, and lead with EAC when talking to the project board. The FD wants to know cash requirements. The project director wants to know total outturn. Same data, different audience, different emphasis.</p></article></div>