Short answer: A common approach works backwards from the likely value of a completed development, deducting the costs and risks of delivering it. This is often called a residual appraisal. Comparable land transactions may also inform professional valuation.
Start with a realistic development scenario
Before discussing value, there must be a credible view of what could be built. The number, size and type of homes, affordable-housing requirements, parking, access, landscaping and sale programme all influence revenue and cost.
Typical appraisal components
Why early figures can change
Before surveys and planning work, assumptions may be broad. Drainage upgrades, contamination, retaining structures, utility diversions, ecology mitigation or a lower housing yield can materially affect viability. Equally, a better design or planning outcome may improve it.
Price mechanisms in agreements
An option or conditional contract may use a fixed price, a formula linked to market value, or a percentage of an agreed valuation subject to deductions. Definitions—particularly planning assumptions, costs and any minimum price—require specialist legal and valuation advice.
Obtain independent valuation advice
A suitably qualified independent valuer can advise the landowner on the proposed basis of value and negotiate with evidence. An online guide cannot value a particular site.
Read ways land may be acquired and the factors that shape site potential.
Authoritative sources and further reading
National policy provides the broad framework, but decisions are normally made against the development plan for the local area unless material considerations indicate otherwise.