Lease Extension Calculator

Calculators are useful as a starting point but they have meaningful limitations.

• They depend on assumptions about deferment rates, relativity and capitalisation that may not match your property.
• They cannot account for all property-specific factors such as condition, location nuances or unusual lease terms.
• Different calculators often produce different answers for the same inputs.
• They do not reflect how negotiations or tribunal decisions actually resolve disputed valuations.

The premium for a lease extension is driven by several inputs:

• Remaining lease length — the most significant single factor, with a sharp inflection at the 80 year threshold.
• Property value — higher values produce larger premiums in absolute terms.
• Ground rent — capitalised into the premium based on the rent profile.
• Marriage value — an additional element triggered below 80 years. Read more.
• Negotiation outcomes — agreed deferment rates and relativity move the figure materially.
• Tribunal evidence — comparable decisions shape what each side can credibly argue.

A calculator estimate is rarely enough on its own when material money is at stake. Consider a more detailed review in any of the following situations:

• Your lease is below 80 years and marriage value applies.
• There is significant disagreement between you and the freeholder on the premium.
• The figure quoted feels unusually high relative to comparable cases.
• You are preparing for or responding to a Section 42 Notice.

See our lease extension cost guide for a deeper breakdown of the drivers. If you already have a quote, you can check whether your lease extension quote is too high by benchmarking it against comparable tribunal outcomes.