50/50 Method Earned Value: Fixed Formula Methods 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-definition">The Definition</a></li><li><a href="#how-the-methods-compare">How the Methods Compare</a></li><li><a href="#when-to-use-each-method">When to Use Each Method</a></li><li><a href="#worked-example-50-50-on-a-8m-fit-out-project">Worked Example: 50/50 on a £8M Fit-Out Project</a></li><li><a href="#when-fixed-formula-creates-problems">When Fixed Formula Creates Problems</a></li><li><a href="#mixing-methods-on-one-project">Mixing Methods on One Project</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 fixed formula method is a shortcut for measuring <a href="/en/earned-value">earned value</a> on activities where detailed progress measurement isn't practical or isn't worth the effort. Instead of tracking percentage complete, you assign a predefined split of the budget at activity start and activity completion. The most common variant is 50/50: credit 50% of the budget when work starts, and the remaining 50% when it's finished. No interim measurement. No arguments about "how far through are you?"</p><p>It sounds crude. On the right activities, it's brilliant.</p><p>Fixed formula methods are part of the <a href="/en/earned-value/definitions">earned value definitions glossary</a>. For the broader EVM framework showing how EV measurement feeds into performance metrics, see the <a href="/en/earned-value/formulas">earned value formulas page</a>.</p><h2 id="the-definition">The Definition</h2><div class="ge-formula-box ge-anim"><span class="ge-formula-label">Formula</span><code>Fixed formula EV = (start %) x BAC at activity start + (completion %) x BAC at activity finish</code></div><p>The most common splits:</p><div class="ge-table-wrap ge-anim"><table class="ge-table"><thead><tr><th>Method</th><th>At Start</th><th>At Completion</th><th>Best For</th></tr></thead><tbody><tr><td><strong>0/100</strong></td><td>0% credited</td><td>100% credited</td><td>Very short activities (under 1 reporting period)</td></tr><tr><td><strong>25/75</strong></td><td>25% credited</td><td>75% credited</td><td>Short activities (1-2 reporting periods)</td></tr><tr><td><strong>50/50</strong></td><td>50% credited</td><td>50% credited</td><td>Medium activities (1-2 reporting periods)</td></tr></tbody></table></div><p>There's no interim measurement. An activity is either not started, started, or complete. Three states. That's it.</p><h2 id="how-the-methods-compare">How the Methods Compare</h2><pre class="ge-ascii-diagram ge-anim"> ACTIVITY BUDGET: £40,000 | DURATION: 6 WEEKS ══════════════════════════════════════════════ Week: 1 2 3 4 5 6 │ │ │ │ │ │ ──────────┼─────┼─────┼─────┼─────┼─────┼── │ │ │ │ │ │ 0/100: £0 £0 £0 £0 £0 £40K ▓░░░░░░░░░░░░░░░░░░░░░░░░░░░░████ Nothing until complete │ │ │ │ │ │ 25/75: £10K £10K £10K £10K £10K £40K ████░░░░░░░░░░░░░░░░░░░░░░░░░████ 25% on start, rest on finish │ │ │ │ │ │ 50/50: £20K £20K £20K £20K £20K £40K ██████████░░░░░░░░░░░░░░░░░░░████ Half on start, half on finish │ │ │ │ │ │ Actual: £5K £12K £20K £28K £35K £40K ██░░░░████░░██████████░░████████████ Real progress (if you measured it) ──────────────────────────────────────────────── KEY INSIGHT: On short activities, the fixed formula averages out across many activities. On long activities, it creates distortion. </pre><p>The beauty of fixed formula is visible in that diagram. Yes, the 50/50 line doesn't match actual progress at any given week. But across 200 activities, the overstatements and understatements cancel out. Some activities are further along than 50% when reported. Some aren't. In aggregate, the total <a href="/en/earned-value/definitions/earned-value">EV</a> converges on reality.</p><h2 id="when-to-use-each-method">When to Use Each Method</h2><p><strong>0/100:</strong> Activities that complete within a single reporting period. Think snagging items, commissioning tests, inspections. If it'll be done before the next report, 0/100 is the honest approach, you either did it or you didn't. I'd estimate 30-40% of activities on a typical fit-out project can use 0/100.</p><p><strong>50/50:</strong> The workhorse method. Best for activities spanning 1-2 reporting periods. Mechanical fix installations, partitioning runs, ceiling grid sections. Activities where measuring interim progress would take more effort than it's worth.</p><p><strong>25/75:</strong> A conservative variant. Useful when you want to avoid front-loading EV on activities that haven't made much real progress. Some client organisations mandate 25/75 as a compromise.</p><p>Here's the critical rule: <strong>don't use fixed formula on activities longer than 2 reporting periods.</strong></p><p>A 50/50 split on a 6-month activity credits half the budget in month 1 and nothing until month 6. That's not EVM. That's fiction.</p><h2 id="worked-example-50-50-on-a-8m-fit-out-project">Worked Example: 50/50 on a £8M Fit-Out Project</h2><span class="ge-worked-label">Worked Example</span><div class="ge-callout ge-anim"><p><strong>Scenario:</strong> A £8M Category A fit-out in Manchester. 14-week programme. The project has 240 activities, of which 200 are under 2 weeks' duration (ideal for fixed formula). The team uses 50/50 for these 200 activities and weighted milestones for the remaining 40 longer activities.</p><p><strong>The 200 fixed-formula activities have a combined budget of £3.2M.</strong></p><p><strong>At the Week 6 report (reporting cut-off: 14 March 2025):</strong></p><div class="ge-table-wrap ge-anim"><table class="ge-table"><thead><tr><th>Status</th><th>Count</th><th>EV Credited (50/50)</th></tr></thead><tbody><tr><td>Not started</td><td>62</td><td>£0</td></tr><tr><td>Started (50% credited)</td><td>48</td><td>48 x avg £16K x 50% = £384,000</td></tr><tr><td>Complete (100% credited)</td><td>90</td><td>90 x avg £16K x 100% = £1,440,000</td></tr><tr><td><strong>Total fixed-formula EV</strong></td><td><strong>200</strong></td><td><strong>£1,824,000</strong></td></tr></tbody></table></div><p><strong>Actual cost for these 200 activities:</strong> £1,780,000 <strong>CPI (fixed-formula activities):</strong> £1,824,000 / £1,780,000 = <strong>1.025</strong></p><p>Is that CPI reliable? For a single activity, no. For 200 activities averaged out, yes. It's a reasonable approximation. The 48 "started" activities are a mix of activities at 10% and 90% progress. On average, they're probably around 45-55% complete. Close enough for 50/50 to work.</p><p><strong>The risk:</strong> 12 of those 48 "started" activities only began in the last 2 days of the reporting period. They're barely at 5% progress but they've been credited 50% EV. That front-loads approximately £96,000 of EV. Over the next report, when some of them complete, the distortion corrects itself. But in week 6 alone, <a href="/en/earned-value/definitions/cost-performance-index">CPI</a> is slightly inflated.</p></div><h2 id="when-fixed-formula-creates-problems">When Fixed Formula Creates Problems</h2><p>The method breaks down in specific situations. Knowing when not to use it is more important than knowing when to use it.</p><p><strong>Long-duration activities with 50/50.</strong> A 6-month groundworks package worth £800,000 gets 50/50 treatment. Month 1: £400,000 of EV credited on day one of work. Months 2-5: no additional EV. Month 6: the remaining £400,000. Your <a href="/en/earned-value/s-curve-tracking">S-curve</a> has a step function, not a curve. That's useless for tracking trends.</p><p><strong>Too many activities in "started" status.</strong> If at any reporting date, more than 40% of your fixed-formula activities are in "started" status, the method is front-loading EV and your aggregate CPI is unreliable. Either the activities are too long for fixed formula, or your team is starting too many activities simultaneously.</p><p><strong>Client EVM reporting.</strong> Some clients (particularly on government projects) won't accept 50/50 for activities above a certain value. MOD and Network Rail have been known to require weighted milestones for anything over £50K. Check the contract requirements before you design your measurement approach.</p><h2 id="mixing-methods-on-one-project">Mixing Methods on One Project</h2><p>Most real projects use a combination of measurement methods. Here's what I'd typically set up:</p><div class="ge-table-wrap ge-anim"><table class="ge-table"><thead><tr><th>Activity Type</th><th>Duration</th><th>Value</th><th>Method</th></tr></thead><tbody><tr><td>Commissioning, testing, inspections</td><td>< 1 week</td><td>< £10K</td><td>0/100</td></tr><tr><td>Install runs, fix-outs, finishes</td><td>1-2 weeks</td><td>< £50K</td><td>50/50</td></tr><tr><td>Major packages (MEP, structural steel)</td><td>> 2 weeks</td><td>> £50K</td><td>Weighted milestones</td></tr><tr><td>Enabling works, groundworks, piling</td><td>> 4 weeks</td><td>> £100K</td><td>% complete or physical measurement</td></tr></tbody></table></div><p>The trick is assigning the right method to each activity at the start, not halfway through when someone realises the EV numbers don't make sense. Build it into the WBS from day one.</p><h2 id="common-mistakes">Common Mistakes</h2><ol><li><strong>Using 50/50 on everything.</strong> Tempting, because it's easy. Disastrous on long activities. If an activity spans more than 2 reporting periods, it needs a different measurement method. Full stop.</li></ol><ol><li><strong>Not defining "started" properly.</strong> Does "started" mean materials delivered to site? First fix commenced? Crew mobilised? If it's ambiguous, you'll get arguments every reporting period. Define it in the EVM procedure before the first report.</li></ol><ol><li><strong>Forgetting that 50/50 front-loads EV.</strong> At any point in time, 50/50 slightly overstates progress (because started activities are credited 50% whether they're at 10% or 80%). Over the full project it washes out. But at month 3 of a 12-month project, your cumulative EV might be 5-8% higher than reality. Factor that into your interpretation of early <a href="/en/earned-value/definitions/cost-performance-index">CPI</a>.</li></ol><ol><li><strong>Applying fixed formula to cost-loaded activities.</strong> If an activity has front-loaded costs (e.g., material procurement happens in week 1, installation in weeks 2-4), the 50% EV credit at start doesn't match the 80% of cost incurred at start. Your CPI for that activity is artificially low early on. For cost-loaded activities, weighted milestones are a better fit.</li></ol><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>Which is better: 50/50 or 0/100?</h3><p>It depends on duration. For activities under one reporting period, 0/100 is more honest, either the work is done or it isn't. For activities spanning 1-2 periods, 50/50 gives you better visibility because you can see work that's in progress rather than waiting for completion. On a project with hundreds of short activities, 50/50 provides a smoother <a href="/en/earned-value/definitions/earned-value">EV</a> curve than 0/100, which tends to create a stepped pattern.</p><h3>Can I use 50/50 on NEC4 contracts?</h3><p>Absolutely. NEC4 doesn't prescribe the EV measurement method. The choice of 50/50, 0/100, weighted milestones, or percentage complete is an EVM implementation decision, not a contractual one. However, the Accepted Programme and activity schedule need to align with your WBS. Make sure the activities in your EVM model match the activities in the programme.</p><h3>How many activities is "enough" for 50/50 to work?</h3><p>The statistical averaging effect works best with 50+ activities using the same method. Below that, individual activity distortions don't wash out and your aggregate EV is less reliable. On a project with only 20 activities, use percentage complete or weighted milestones instead.</p><h3>What about 20/80 or 40/60 splits?</h3><p>You can use any split you like. 20/80 is common in aerospace and defence. 40/60 appears in some government frameworks. The principle is the same: assign a start percentage and a completion percentage. The more conservative the start percentage, the less front-loading of EV. Pick the split that best represents the typical progress profile of your activities.</p></article></div>