RICS Knowledgebase

The Global Red Book 2025 has Marriage Value in the definitions and in turn refers to the IVS which calls it at 10.28 Synergistic Value.

Both the Red Book and IVS are principles based and will not explain 'how'. 

There are sections on Synergistic Value in Modern methods of valuation by Shapiro. To browse the text if you don't already have access to the ebook service (free in your RICS membership) email knowledge@rics.org to get access.

isurv (subscription required) has some worked examples Land: synergistic value of merging interests | Synergistic value: worked examples | isurv

 
Note about Leasehold reform in England

The Leasehold and Freehold Reform Act 2024 (LAFRA) has introduced significant changes to the calculation of lease extension premiums, including the abolition of marriage value. This change is part of a broader effort to make the leasehold system more fair and transparent. Arc Time Freehold Income Authorised Fund & others v Secretary of State for Housing, Communities & Local Government [2025] EWHC 2751 (Admin), a landmark ruling in the High Court confirms that the Government’s reforms are lawful however they are subject to ongoing challenges by large freeholders and possible appeal. Secondary legislation to bring these into force have therefore not yet been laid and we do not yet know when this might happen. We have a leasehold reform hub here which is following significant changes and the RICS are in regular contact with a range of stakeholders including MHCLG. 

This Commons Library paper is kept upto date with developments 

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This also might be useful - What is ‘Marriage Value’ in Property Valuation? - Horizon Management

Last updated April 2026