6.2 Business Case: Desirability, Viability & Achievability

The Three Tests

The Business Case practice exists to answer one question throughout the project: is this still a worthwhile investment? PRINCE2 frames that question through three tests applied at every decision gate:

1. Desirability — is the project worth doing? The expected benefits outweigh the dis-benefits and align with organisational strategy.
2. Viability — can the project be done? The solution is technically and organisationally feasible within an acceptable cost and timeframe.
3. Achievability — can we deliver it? The organisation has (or can acquire) the capability, capacity, skills, and resources to realise the outcome.

Desirability is a strategic judgement, viability is a feasibility judgement, and achievability is a delivery-capability judgement. A project can be desirable but not viable (the technology does not yet work at scale), or viable but not achievable (the team lacks the skills to deliver it). All three must hold.

The Executive as Driver

The Executive is the named driver of the Business Case practice. Only the Executive owns the Business Case, presents it at stage boundaries, and answers for benefit realisation. This single accountability prevents a common failure mode: a project sponsored by committee where no one is willing to withdraw funding when the case weakens. The Executive is supported by Project Assurance (who challenge the case independently) and Senior User/ Senior Supplier (who contribute benefit and cost evidence respectively), but ownership sits with the Executive.

Contents of a Business Case

A PRINCE2 Business Case is structured around the following elements. They map to the investment appraisal and options analysis that underpin the document:

v7: Sustainability and ESG targets

v7 adds explicit sustainability targets and ESG (environmental, social, governance) goals as content the Business Case should record where relevant. Rather than a standalone document, sustainability objectives are captured inside the Business Case so they sit alongside financial and strategic benefits, and are tracked through a linked sustainability management approach. This prevents 'green' commitments being made at initiation and then quietly dropped once funding is approved.

Options Analysis and Investment Appraisal

Before the recommended option is documented, the Business Case performs options analysis: a short list of credible options (including do nothing) is compared against selection criteria. The preferred option is then validated by an investment appraisal technique appropriate to the organisation — payback period for short-cycle decisions, net present value (NPV) for longer horizons, or ROI where cash-flow timing is less material. The do-nothing option is always retained as the baseline so reviewers can see the delta the project creates.

What Makes a Business Case 'Valid'

For the Project Board to approve a stage, the Business Case must be valid — that is, current, internally consistent, and still passing the three tests. A case becomes invalid when costs overrun beyond tolerance, when benefits shrink or move beyond the project's control, when a strategic dependency disappears, or when achievability is undermined by loss of key resources. At that point the Executive must either rework the case or recommend project closure rather than let an invalid case carry on funding work.

Worked Example — Applying the Three Tests

A hospital trust proposes a new electronic prescribing system. Desirability: the trust's strategy commits to reducing medication errors by 40%, and the system is expected to cut error rates by 55%, so desirability is strong — the benefits outweigh the dis-benefits (clinician retraining time, temporary dual-running) and align with strategy. Viability: the vendor's product is deployed in 12 comparable trusts and passes clinical safety review, so the solution is technically and organisationally feasible — viability holds. Achievability: the trust's informatics team has 4 of the 8 full-time equivalents the implementation needs and cannot recruit the rest inside the planned timescale. Achievability fails. The correct response is not to kill the project but to re-scope it (a phased rollout that fits the available team) or to extend the timescale so recruitment can complete. The three tests diagnose which dimension is weak, and that diagnosis drives the corrective action — a single 'not worthwhile' verdict would not tell the Board what to fix.

Choosing an Investment Appraisal Technique

The appraisal technique is not a free choice — it follows the decision horizon and the organisation's finance policy:

The do-nothing option is always retained as the baseline so reviewers can see the delta the project creates, not the absolute return. A common exam trap is an option that appraises only the preferred option without comparing it to do-nothing — that is an incomplete appraisal.

Common Exam Traps for the Business Case

• Adding 'acceptability' as a fourth test. There are only three: desirability, viability, achievability. Any option introducing 'acceptability' or 'affordability' as a peer test is wrong.
• Assigning the Business Case to the Project Manager. The Project Manager maintains the document, but ownership and accountability sit with the Executive. An option that says 'the Project Manager owns the Business Case' confuses maintenance with ownership.
• Forgetting dis-benefits. A valid Business Case records negative consequences for parts of the organisation, not just benefits. An option that lists only benefits and costs is incomplete.
• Dropping sustainability in v7. Where ESG targets are relevant, v7 expects them recorded in the Business Case and tracked through a sustainability management approach — not appended as an afterthought.