A business case is a concise, data-driven statement that justifies why a project deserves time, budget, and attention, by connecting a specific problem to its financial impact on the organization.
In Six Sigma, it is written during the DMAIC Define phase and typically becomes the opening section of a project charter, but it is a distinct document with its own job: proving the cost of the problem is large enough to justify the cost of solving it.
Most explanations describe a business case only in vague terms (“explain why this matters”), which is exactly the gap this guide closes. Below is the actual structure, a worked financial calculation showing how to size a problem in dollars, and the difference between a business case, a problem statement, and a project charter, three terms that get confused constantly.
| Document | What It Answers | When It’s Written | Typical Length |
| Business Case | Why does this problem matter financially, and why now? | Before or at the start of Define phase | 3 to 5 sentences |
| Problem Statement | What exactly is broken, where, and by how much? | Define phase, after the business case | 2 to 4 sentences |
| Goal Statement | What specific, measurable target will the project hit? | Define phase, after the problem statement | 1 to 2 sentences |
| Project Charter | Who is doing this, with what scope, timeline, and resources? | Define phase, compiling all of the above | 1 to 2 pages |
Table of contents
Key Takeaways
- A business case exists to answer one question convincingly: is the cost of this problem large enough to justify the cost of fixing it? Everything else is supporting detail.
- The strongest business cases use a specific dollar figure, not a vague statement of urgency. “This defect rate costs us $460,000 annually” earns approval faster than “this defect rate is a concern.”
- A business case is not the same document as a project charter. The business case is typically one short section within the charter, not the entire document.
- The most common business case formula follows a simple pattern: defect rate (or failure rate) × cost per occurrence × annual volume = estimated annual cost of the problem, giving leadership a defensible number without requiring a full root cause investigation first.
- A business case only needs to be directionally accurate, not perfectly precise, at this stage. Detailed data collection happens in the Measure phase; the business case just needs enough evidence to justify starting the project.
What Is a Business Case?
A business case is a short, evidence-based statement that connects a specific operational problem to its financial cost, and proposes that a project be approved to address it. Its entire purpose is persuasive: convince a sponsor, budget holder, or leadership team that a problem is worth solving right now, using numbers rather than opinions.
According to guidance on writing Six Sigma business cases, a business case is a concise, data-driven document that justifies the need for a project by defining a business problem, its financial impact, and the expected benefits of the proposed solution.
Notice what is not in that definition: a detailed root cause analysis, a full project plan, or a finished solution. A business case is deliberately an early, rough-cut argument, not a completed investigation.
This is where many first-time Green Belts get the format wrong. A business case that reads like an essay, background, history, multiple paragraphs of context, buries the one thing a busy sponsor actually needs: the dollar figure. A strong business case is closer to a headline than a report.
Public, Onsite, Virtual, and Online Six Sigma Certification Training!
- We are accredited by the IASSC.
- Live Public Training at 52 Sites.
- Live Virtual Training.
- Onsite Training (at your organization).
- Interactive Online (self-paced) training,
Business Case vs. Project Charter: Where It Actually Fits
This is one of the most common points of confusion in Six Sigma training, and it is worth resolving clearly. A project charter is the complete governing document for a Six Sigma project: it includes the business case, the problem statement, the goal statement, project scope, team roles, timeline, and often a high-level project plan.
The business case is one section inside that charter, usually the opening section, not a separate standalone deliverable in most organizations. Think of the relationship this way: the business case answers “why should this project exist at all,” while the rest of the charter answers “how, exactly, will this project run.”
A charter without a strong business case section is a plan with no justification behind it; a business case without the rest of the charter is a pitch with no execution plan attached.
Also Read: How to Write a Six Sigma Business Case
The Anatomy of a Strong Business Case
A well-constructed business case consistently includes four elements, regardless of industry or project size.
1. The Problem, Stated at a Business Level
Not a detailed technical description, a plain statement of what is underperforming and against what standard. “Our accounts payable process is not meeting our 30-day payment goal” is a business-level problem statement; a technical breakdown of exactly why comes later, in Measure and Analyze.
2. The Financial Impact
This is the section that actually moves a business case from “interesting” to “approved.” A specific dollar estimate, even a rough one, gives a sponsor something concrete to weigh against the cost of running the project.
3. The Strategic Connection
A brief note tying the problem to a broader organizational goal, customer satisfaction, cost reduction targets, compliance requirements, makes it clear the project is not an isolated fix but part of something leadership already cares about.
4. The Cost of Inaction
The most frequently missing element. A business case that only describes the upside of fixing the problem is weaker than one that also states what continuing to do nothing will cost the organization over the same period.
The Formula: How to Size a Problem in Dollars
This is the part most generic explanations skip entirely, and it is the single most useful thing a business case writer can learn. A defensible, back-of-envelope dollar estimate follows a simple structure:
Occurrence rate × cost per occurrence × annual volume = estimated annual cost
A worked example: A manufacturing line is running a 20 percent defect rate. Each defective unit costs $150 to rework or scrap, once labor, materials, and lost throughput are factored in. The line produces 35,000 units per year. The calculation: 0.20 × $150 × 35,000 = $1,050,000 in estimated annual cost from this single defect issue.
That single number does more persuasive work than several paragraphs of qualitative description. It also does something else valuable: it gives the team an early filter for prioritization. A separate issue on the same line costing an estimated $18,000 per year, using the same formula, is very likely not worth the time and resources of a formal Six Sigma project, while the $1,050,000 issue clearly is.
Also Read: How Lockheed Martin Used Six Sigma to Save Billions: A Real Case Study
Real Business Case Examples Across Industries
Manufacturing: Defect Rate and Rework Cost
A production line business case built around the formula above: defect rate, cost per defective unit, and annual volume, producing a clear annualized cost figure that justifies launching a formal DMAIC project.
Healthcare: Patient Wait Time and Readmission Cost
A hospital business case might state that emergency department wait times exceeding a target threshold correlate with a measurable increase in 30-day readmissions, each carrying an estimated cost in penalties and additional care, producing an annualized financial exposure figure.
Financial Services: Processing Errors and Compliance Risk
A bank’s business case for a loan processing project might combine a direct cost (hours spent correcting errors, multiplied by loaded labor cost) with a risk-adjusted estimate of potential regulatory penalties, giving leadership both a hard cost and a risk-based justification.
Retail: Return Rate and Lost Margin
A retailer’s business case for a packaging redesign project might calculate the annual cost of damage-related returns, using the same occurrence-rate-times-cost-times-volume formula, to justify investment in a packaging engineering fix.
Common Mistakes When Writing a Business Case
- Leading with narrative instead of numbers. A sponsor skimming a charter should be able to find the dollar figure in the first two sentences, not buried in paragraph four.
- Waiting for perfect data before writing anything. A business case only needs a directionally accurate estimate; detailed data collection is the Measure phase’s job, not the business case’s.
- Confusing the business case with the problem statement. The business case argues why the problem matters financially; the problem statement describes what, where, and how much, without the persuasive framing.
- Omitting the cost of inaction. A business case that only describes potential savings, without stating what continuing the current state costs, is a weaker argument than one that shows both sides.
- Writing a business case for a project too small to justify formal DMAIC. Not every problem, even a real one, is worth a full certified project; the dollar-sizing formula helps filter out issues better suited for a Just-Do-It fix instead.
Frequently Asked Questions on Business Case
What is the difference between a business case and a project charter?
A business case is a short, persuasive section that justifies a project financially. A project charter is the complete governing document for the project, and the business case is typically its opening section, not a separate document.
How detailed does a business case need to be?
Not very. A business case should be 3 to 5 sentences, with a specific dollar estimate, rather than a fully researched report. Detailed investigation happens later, in the Measure and Analyze phases.
What formula is used to estimate the financial impact in a business case?
A common approach multiplies the occurrence rate of a problem by the cost per occurrence, then by annual volume, producing an estimated annual cost. This gives a defensible, directionally accurate figure without requiring a completed root cause investigation first.
Who writes the business case in a Six Sigma project?
Typically the project sponsor or the assigned Green Belt or Black Belt drafts the business case during the Define phase, often in collaboration with the project’s champion, before the full charter is finalized.
Can a business case change after the project starts?
Yes. The business case is built on early, directionally accurate estimates. As the Measure phase produces more precise data, the financial impact figure is often refined, though the original estimate should have been close enough to justify starting the project.
Final Words
A business case does one job: prove that a problem’s cost is large enough to justify the cost of fixing it, in language a busy sponsor can act on in under a minute. The strongest ones lead with a specific dollar figure, built from a simple occurrence-rate-times-cost-times-volume calculation, rather than a long narrative explanation.
Six Sigma Development Solutions Inc. teaches business case development as part of a complete DMAIC Define phase, across onsite, live virtual, public, and online formats, IASSC accredited, rated 5 stars on Google Reviews, with 5,322+ professionals certified across 600+ organizations in 52 cities. View our upcoming Green Belt and Black Belt training schedule and learn to build a business case that gets approved.
About Six Sigma Development Solutions, Inc.
Six Sigma Development Solutions, Inc. offers onsite, public, and virtual Lean Six Sigma certification training. We are an Accredited Training Organization by the IASSC (International Association of Six Sigma Certification). We offer Lean Six Sigma Green Belt, Black Belt, and Yellow Belt, as well as LEAN certifications.
Book a Call and Let us know how we can help meet your training needs.
