In PRINCE2, the Business Case is the North Star: it answers “Is this project still worth doing?” Because viability can drift, PRINCE2 mandates regular, event-driven checks—not a “set-and-forget” document.

Ownership & Accountability

• Accountable: Executive (Project Board).
• Responsible for maintenance: Project Manager (on behalf of the Executive).
• Assurance: Senior User validates benefits; Senior Supplier validates feasibility/costs; Project Assurance challenges assumptions.

Minimum Cadence (PRINCE2-compliant)

1. Project Initiation (PID approval):
   Create/confirm the Business Case and Benefits Management Approach.
2. End of Every Stage (Managing a Stage Boundary):
   Formal review and update before the next Stage Plan is approved. The Project Board re-confirms continued business justification.
3. Exception Situations (Exception Assessment):
   Immediate review if forecast breaches tolerances (time/cost/quality/scope/benefit/risk). Approve an Exception Plan only if the updated case still stacks up.
4. Benefits Reviews (Post-Project):
   Conduct benefits realization reviews per the Benefits Management Approach (e.g., T+3 months, T+6 months, T+12 months after go-live).

If nothing material changes within a stage, the Business Case can remain stable until the next end-stage review.

Materiality Thresholds (good practice):

• Cost: ±10% stage EAC variance or any change > the project cost tolerance.
• Schedule: Slippage > 10% of stage duration or impacts benefits window.
• Benefits: ≥5% downside to year-1 benefits or deferral of key benefit beyond payback horizon.
• Risk: Exposure (P×I) increases by one risk band (e.g., Medium → High).
• Scope: Change to MVP/critical product descriptions affecting benefits realization.

When a threshold is exceeded, update Business Case immediately and, if viability weakens, escalate to the Project Board.

What Exactly to Update

• Financials: Revised CAPEX/OPEX, NPV, IRR, Payback period.
• Assumptions & Dependencies: New lead-times, vendor constraints, regulatory shifts.
• Benefits Profile: Timing, magnitude, measurability; confirm owners.
• Risk Exposure: Top threats/opportunities and mitigations; residual risk.
• Options Analysis: “Do nothing / Do minimum / Do something” comparison refreshed.
• Sensitivity & Scenario Testing: Best/base/worst case with clear triggers.

Stage-by-Stage Playbook

Start-Up & Initiation

• Draft outline Business Case → evolve to a full Business Case in the PID.
• Lock the Benefits Management Approach (who measures what and when).

Stage 1…N (Delivery Stages)

• During the stage: scan Highlight Reports; if thresholds trip, update now.
• End of stage: run End Stage Report + refreshed Business Case; Board decides “Continue / Change / Stop.”

Final Delivery Stage

• Confirm benefits that can be measured at project closure; schedule the rest post-project.
• Hand off the Benefits Management Approach to Operations/Benefits Owner.

Post-Project

• Execute benefits reviews on the agreed dates; update the Business Case record with actuals vs forecast; capture lessons.