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Project Detailed Business Case (DBC)

When a Detailed Business Case is needed

For projects that require a two-stage business case process, a Detailed Business Case is developed following approval of the Indicative Business Case.  Detailed Business Cases are also developed for significant projects within programmes, or for programme tranches, following approval of the Programme Business Case.

The DBC documents further analysis of the Recommended Way Forward proposed in the Indicative Business Case (or whatever alternative way forward has been approved by decision-makers).

The DBC appraises in detail the social, wellbeing and economic costs, benefits and risks of the short-listed options to identify the preferred option; the option which offers optimum public value for delivery of the project.  This preferred option is documented in the DBC and is taken to decision-makers for agreement before going to market for a formal proposal.

Purpose of the Detailed Business Case

The Detailed Business Case recommends a preferred option that optimises value for money, and seeks approval from decision-makers to finalise the arrangements for successful implementation.  For state sector projects, approval of the Detailed Business Case secures funding as ‘tagged contingency’.

The decision to develop the Detailed Business Case typically follows from approval of an Indicative Business Case recommendation to proceed with the preferred way forward.  The Detailed Business Case:

  • revisits and confirms the strategic case developed in the Indicative Business Case
  • identifies the preferred option which optimises value for money, by undertaking a more detailed analysis of the costs, benefits and risks of the short-listed options
  • prepares the proposal for procurement
  • plans the necessary funding and management arrangements for the successful delivery of the project
  • informs a proposal to decision-makers to seek agreement to approach the market and finalise the arrangements for implementation of the project.


Supporting collateral Detailed Business Case
Guidance and template: to understand the development process and document the results Detailed Business Case - Template & Guidance (Apr 2021) (DOC 2,111 KB)
A3 presentation bbc-detbus-pr-v2 (PPT, 421KB)
Reviewer assessment tool Detailed Business Case - Reviewer Assessment Tool (March 2021) (DOC 391 KB)


All significant projects, of all types, are required to have and follow Assurance Plans appropriate to their scale and risk.

ICT-enabled state sector projects and programmes assessed as High Risk are required to prepare costed assurance plans.  Contact [email protected]

Programmes and projects assessed as High Risk must include Gateway Reviews in their Assurance plans. They are normally required to have a review (Gate 2: Delivery Strategy) as the Detailed Business Case nears completion.  There is a 6-8 week lead time for contracts and logistics, so get in touch early: [email protected] 

Next steps

Approval of the Detailed Business case results in the allocation of ‘tagged contingency’.  This is effectively agreement by Cabinet to fund the project as part of the next Budget process (although not necessarily to draw down the full funding), and by the agency a commitment to deliver the project and its associated benefits, as documented in the Cabinet Minute.  

Decision-makers may put conditions on the approval, making it subject to the results of an approach to market.  For instance:

  • Decision-makers may delegate approval of the next business case (Implementation Business Case, ImBC) to a subsidiary body (eg council committee, or Joint Ministers), if costs remain close to the DBC estimates.
  • Decision-makers may require that, if the costs finalised through an RFP differ from the DBC costs by more than a specified amount/proportion, the ImBC (or a Cabinet paper) must come back to them for a new approval
  • Once the Detailed Business Case has been approved, a Request for Proposal (RFP) may be issued to the market, except for proposals that are likely to result in a non-traditional procurement.  Note that
  • Agencies that are planning any significant investments (including any arrangements with Local Government Authorities seeking Crown funding or support) should evaluate all procurement options, including considering the use of Public Private Partnerships where appropriate and consistent with Government policy. Note that the current government (2017-2020) does Government does not support the continued use of PPPs in the health and education sectors.

The project also starts work on the Implementation Business Case (ImBC), which documents finalised arrangements and costs.

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Last updated: 
Tuesday, 16 November 2021