Lease Extension Calculator: Estimate Your Premium (2026)
Estimate what a statutory lease extension would cost under the Leasehold Reform, Housing and Urban Development Act 1993. Enter three figures: years remaining, the flat's long-lease value, and your ground rent, and this calculator returns a likely premium RANGE (a surveyor never quotes a single number, so neither do we), shows whether the 80-year marriage-value cliff applies, and lets you check the building's tribunal dispute history before you serve notice. Instant, no email wall.
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How this lease extension calculator works
Enter your unexpired lease years, the flat's value with a long lease (or share of freehold), and your annual ground rent. The tool applies the statutory valuation under Schedule 13 of the Leasehold Reform, Housing and Urban Development Act 1993 (LRHUDA 1993) and returns a premium as a low–central–high range. Every top lease-extension calculator on the web shows a single number; a surveyor never would, because the answer turns on negotiated relativity and the exact lease terms. We show the range, the marriage-value treatment, and the assumptions behind every figure.
Your result explained
The premium is built from three parts. Term loss is the ground rent the freeholder gives up, capitalised at roughly 7%. Reversion loss is the value of the freeholder eventually getting the flat back, deferred to today at the 5% Sportelli deferment rate. Marriage value is half the value created by extending, and it is added only when the lease is below 80 years. If your lease is above 80 years the result will say so and exclude marriage value; if it is below, the marriage-value line lights up red, because that is the number that grows the longer you wait.
The 80-year cliff: why every year counts
The single most important fact in lease extension is the 80-year cliff. At 80 years and above, marriage value is deemed nil. The moment the lease falls below 80 years, you must pay the freeholder 50% of the value uplift, and that figure rises steeply as the term shortens. The calculator draws this as a premium-versus-years curve with your position marked, so you can see exactly how much a delay costs.
| Unexpired term | £200,000 flat (no ground rent) | £500,000 flat (no ground rent) |
|---|---|---|
| 90 years | ~£3,000–£5,000 | ~£7,000–£12,000 |
| 82 years | ~£6,000–£9,000 | ~£14,000–£22,000 |
| 79 years (just below cliff) | ~£9,000–£14,000 | ~£22,000–£34,000 |
| 70 years | ~£14,000–£22,000 | ~£34,000–£55,000 |
Illustrative ranges from the calculator's own method (deferment 5%, ground-rent yield 7%, graph relativity); your figure depends on ground rent and the negotiated relativity. An estimate, not a valuation.
What this means for your purchase
If you are buying a flat, a short lease is both a cost and a negotiating lever: the premium you'll pay to extend should come off your offer. A lease under 80 years also narrows the pool of lenders willing to mortgage it. Work out the likely premium here, then read whether the lease is short enough to walk away from in our guide to whether a lease is too short to buy, and run a HouseCheckup report on the address to see the wider picture.
Check this building's dispute history before you extend
A freeholder or managing agent with a history of First-tier Tribunal (Property Chamber) disputes can be harder to negotiate a lease extension with, and the same building often shows up across service-charge and management cases. HouseCheckup holds 16,880 published tribunal decisions keyed to postcode and building, something no other lease-extension calculator links to. Before you serve a Section 42 notice, check whether your building has a tribunal dispute history.
Is there an official government lease extension calculator?
No. There is no lease-extension calculator on gov.uk. The widely-cited free tool belongs to LEASE (lease-advice.org), a government-funded charity, not a government service. Northern Ireland publishes an Excel template for its own (different) scheme. So while many searchers look for a "government" or "gov" calculator, none exists; treat every online estimate (including this one) as a guide and confirm with a RICS valuation.
Land Registry & registration fees
Beyond the premium and professional fees, the extended lease must be registered at HM Land Registry, which charges a scale fee based on the property value (commonly £20–£150 for a registered title under the standard scale). Your solicitor handles this as part of completion. See our buying costs calculator for how registration and legal fees fit the wider cost of a purchase.
How the process works (Section 42 to tribunal)
The statutory route: own the flat for two years, obtain a RICS valuation, serve a Section 42 notice on the freeholder proposing a premium, then negotiate. If you can't agree within the statutory window, either side can apply to the First-tier Tribunal to determine the premium, a process that adds a few months. Most cases settle by negotiation; the published tribunal decisions exist precisely because some don't, which is why a freeholder's dispute history is worth knowing.
The law is changing: Leasehold and Freehold Reform Act 2024
The Leasehold and Freehold Reform Act 2024 will, once commenced, abolish marriage value, standardise the valuation rates, and let leaseholders take a 990-year extension at a peppercorn rent, which is materially cheaper for most. However, the key valuation provisions are not yet in force and, given the secondary legislation and consultation still required, are unlikely to commence before 2027. Until then, the LRHUDA 1993 method this calculator uses remains the law. We will update the engine when the new rules take effect.
Get the full picture for the address
Lease length is one factor among many. The HouseCheckup Complete report pulls the leasehold context, alongside true running costs, flood, EPC, crime and more (15+ official-source checks), for a specific address, so you go into the purchase or the extension knowing exactly what you're taking on. This estimate is an estimate, not a RICS valuation. Instruct a surveyor before serving notice.
Frequently asked questions
How much does it cost to extend a lease?
Why does lease length matter below 80 years?
Is there an official government lease extension calculator?
How is the premium calculated?
What is the process and how long does it take?
What ground rent should I enter if I don't know it?
Will leasehold reform change extension costs?
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