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Free lease extension calculator · UK flats

What will it cost to extend your lease?

Model a lease-extension premium under the pre-commencement method, including term, reversion and marriage value where the model applies it. Compare a separate 2024 Act scenario. No sign-up; not a formal valuation or statement of current law.

Your flat
Roughly what it'd be worth with a fresh/long lease
Check your lease or title
Current annual ground rent

Estimated premium

To extend (mid estimate)
Likely range
What makes it up
Loss of ground rent (term)
Loss of reversion
Marriage value (pre-commencement model)
2024 Act scenario
Illustrative premium without marriage value
Estimate using a term + reversion + marriage-value model (deferment 5%, ground-rent capitalised 7%, relativity curve) and a separate illustrative 2024 Act scenario. At the official 7 September 2026 review, the relevant valuation changes still required consultation, secondary legislation and commencement. Check the current GOV.UK position. Real premiums require specialist valuation and legal advice.
Before you trust that number

The premium hinges on what your flat is actually worth.

Guess the value high and the premium rises; guess it low and you may under-budget. PropertyPredator can show nearby HM Land Registry sold-price evidence and matched floor-area context where available, so you can test whether the deal still works after an estimated extension cost.

✓ Nearby sold-price evidence✓ £/ft² & £/m² where matched✓ Indicative valuation context✓ Deal model after the estimated premium
Check the flat with evidence — free account →
Want buy-the-freehold mode and both legal-basis scenarios? Open the Leasehold Value Engine →
Free to start. No card required for the free tools.

Lease extension — questions

Why is 80 years shown?

The calculator's pre-commencement model adds marriage value below 80 years. The 2024 Act provides for that element to be removed, but commencement and technical rules are time-sensitive. Check the current official position and take specialist advice.

How accurate is this estimate?

It uses stated deferment, capitalisation and relativity assumptions to produce a broad budgeting range. Real premiums depend on the lease, valuation date, professional evidence, negotiation and the law then in force. It is not a quote.

Is this for flats or houses?

This estimates the premium for a flat lease extension. Leasehold houses follow a different process. Always take professional advice for your specific lease.