Lease extension cost guide

Estimate the range, see every assumption and verify the lease facts.

Use the lease dates and ground-rent schedule with property-value evidence to produce a current-law planning range. The result is a guide, not a valuation, offer or negotiation figure.

The surveyor's model

The calculation is maths. The evidence selects the inputs.

A specialist valuer calculates the landlord's lost ground-rent income, delayed reversion and, where current law requires it, marriage value. They then support the rates and property values with the lease, valuation assumptions, comparable transactions and current case law.

Facts LEASE-iQ can supply

Lease commencement and expiry dates
Unexpired term at a stated valuation date
Current In plain EnglishRent reserved by a lease. It is separate from service charges and administration charges.Read the official guidance and full review schedule
Relevant variations and intermediate lease interests found in the documents checked
Clause, page and source status for each lease fact

Evidence the customer or valuer supplies

Long-lease value supported by comparable local sales
Current short-lease value, where professionally assessed
Location and property characteristics
Improvements to disregard, with evidence of who carried them out
Any additional loss or special circumstance outside the standard model
Professional and procedural cost estimates

Evidence standard: LEASE on valuation assumptions, what a valuer needs and RICS on specialist leasehold reform valuation.

Prepare the inputs in LEASE-iQ

Get the document facts in one source-cited answer

Copy this prompt into LEASE-iQ after selecting the relevant signed lease and any deeds of variation. It asks for facts and missing evidence, not a valuation or legal conclusion.

Prepare the lease-extension calculator data pack for this flat in England or Wales, as at [CALCULATION DATE].

Review the signed lease, every deed of variation and any intermediate or superior lease supplied. Do not infer missing facts.

Return:
1. Jurisdiction.
2. Property and interest reviewed.
3. Lease commencement date.
4. Original term.
5. Contractual expiry date.
6. Unexpired term at [CALCULATION DATE], showing the date arithmetic.
7. Current annual ground rent.
8. Every ground-rent review date, interval, amount or formula, including RPI wording and any caps or floors.
9. Parties and any intermediate landlord or superior interest found in the reviewed documents.
10. Variations affecting term, rent or parties.
11. Any wording relevant to improvements or alterations, without deciding whether an improvement must be disregarded for valuation.
12. Current legislation status relevant to the calculation, separating operative law from proposed or uncommenced reform.

For every document-derived answer show: value, document, clause, page, short source wording, confidence and whether manually verified.

Then produce:
A. A calculator-ready table.
B. A list of missing or ambiguous data.
C. A list of information that must come from outside the lease, including long-lease value, short-lease value, comparable sales, qualifying improvements, valuation rates and any additional loss.

Do not estimate property value, relativity, capitalisation rate, deferment rate, eligibility, premium, negotiation figure or legal outcome. If the documents checked do not establish a point, say "not established from the reviewed sources".

What official data can add

HM Land Registry Price Paid Data can help identify possible transactions and the UK House Price Index can provide broad time context. They do not establish that a sale is genuinely comparable, its exact lease length, condition or the correct valuation assumptions. Use them to prepare evidence, then confirm the selection.

HM Land Registry Price Paid Data and UK House Price Index downloads.

Numerical planning guide

Estimate a current-law lease-extension range.

Use dated lease facts, property-value evidence and visible valuation assumptions. The result is a budgeting guide. It is not a valuation, offer, Section 42 figure, negotiation figure, legal opinion or tribunal evidence.

1. Lease dates

LEASE-iQ can return these document facts with the clause and page. Enter them manually here because automatic transfer is not live. This website owns the arithmetic and the displayed planning range.

Planning or Section 42 notice date For a formal claim, use the Section 42 notice date. Otherwise this is a planning date. Contractual lease expiry date Use the signed lease and any deed that changed the term.

2. Property-value evidence

Enter a defensible range, not an asking price. Comparable sales still need selection and verification.

Value after a 90-year extension, lower (£) Value after a 90-year extension, upper (£) Current short-lease value, lower (£), if professionally assessed Current short-lease value, upper (£), if professionally assessed

If the lease has 80 years or fewer and no current-value range is supplied, the guide uses the broad displayed relativity band. Market evidence at or near the valuation date should replace that band where available.

3. Ground-rent schedule

Model the clause actually in the lease. For an index-linked clause, enter a visible planning assumption for future increases.

Current annual ground rent (£) Review pattern Years until next review Review interval in years Increase at each review (%) Used only for the percentage pattern. Enter the assumed increase produced by the lease formula. It is not an inflation forecast.

4. Visible valuation assumptions

The rates are not prescribed universal defaults. This broad planning interval is editable because property and investment evidence can justify a different rate.

Capitalisation rate, lower (%) Capitalisation rate, upper (%) Deferment rate, lower (%) Deferment rate, upper (%)

5. Other costs

Keep professional and procedural costs separate from the premium.

Other costs, lower (£) Other costs, upper (£)

I understand that this is an indicative planning range and not a professional valuation, offer, Section 42 figure or negotiation figure.

Indicative current-law premium range

Premium plus entered other costs

Unexpired term at the entered date

Lost ground-rent income

Delayed reversion

Marriage value contribution

Other compensationNot modelled

Assumptions used

Inputs and assumptions used for this result. Nothing is hidden.
Input	Range or status

What to verify next

Use LEASE-iQ with this lease

Current law and planned reform

The current 90-year method is used.

This guide does not model the planned 990-year term, removal of marriage value or future prescribed valuation rates. Those reforms are not used until the relevant provisions are operative.

Government status LEASE valuation guide

Model boundary

Available data improves the guide. It does not remove judgment.

HM Land Registry data can help identify possible sales. It does not establish lease length, condition or true comparability. Capitalisation, deferment, relativity, improvements and special losses can materially change the result.

Model version BT-LEX-2026-08-24. Law and public sources checked 26 August 2026. Calculations stay in this browser and are not uploaded or stored.