UK Lease Extension Premium Calculator (Indicative)
Get a quick estimate for a statutory 90-year lease extension in England and Wales. This tool uses a simplified valuation model used by surveyors: term value + reversion + marriage value (where applicable).
Important: This is an educational estimate, not a formal valuation. Always get advice from a qualified leasehold valuer and solicitor before serving a Section 42 notice.
How to use this lease extension calculator UK
This lease extension calculator is designed to give you a practical starting point before speaking with a surveyor. Enter your flat value, years left on the lease, ground rent, and rate assumptions. The output shows an estimated premium and your likely total budget including professional fees.
The model follows the key valuation components commonly used in UK lease extension work:
- Term value (the present value of future ground rent lost by the freeholder)
- Reversion value (the value of getting the property back at lease expiry)
- Marriage value (typically payable where the lease has under 80 years remaining)
What each calculator input means
Flat value (long lease value)
This is the approximate market value of your property assuming a long lease (or virtual freehold equivalent). Most valuers use this as the baseline “after extension” value.
Unexpired years
The number of years left drives the premium heavily. As the term drops, the landlord’s reversion becomes more valuable and marriage value risk increases.
Ground rent and capitalisation rate
Ground rent is converted into a present value using the capitalisation rate. A lower rate generally increases the landlord’s term value, and therefore the premium.
Deferment rate
This is used to discount the value of the freeholder’s future right to possession (reversion). Small changes in deferment assumptions can move the estimate significantly.
Relativity
Relativity is the value of the existing short lease as a percentage of long-lease value. Lower relativity increases marriage value. If you leave the field blank, this page applies an automatic, broad-brush estimate curve.
Why the 80-year lease threshold matters so much
In many statutory valuations, once a lease drops below 80 years, marriage value can become payable. That often causes a step-change in premium. In plain terms: extending before 80 years can be materially cheaper than waiting.
That’s why leaseholders often monitor their term early and take advice well before the deadline zone.
Statutory vs informal lease extension
Statutory route (Leasehold Reform, Housing and Urban Development Act 1993)
- Adds 90 years to the existing term
- Ground rent becomes a peppercorn (effectively zero)
- Legal framework and timelines are defined
- Disputes can be referred to the Tribunal
Informal route (negotiated directly with freeholder)
- Can be faster in straightforward cases
- Terms are negotiable and may vary widely
- May include higher revised ground rent if not carefully reviewed
- Requires careful legal scrutiny before agreeing
Other costs beyond the premium
A common mistake is budgeting only for the premium. In reality, you should allow for:
- Your solicitor’s fee
- Your valuer’s fee
- Freeholder’s reasonable legal and valuation costs (usually payable by leaseholder in statutory claims)
- Land Registry and disbursements
- Potential Tribunal costs if there is a dispute
The calculator includes a simple fees section to help you estimate a fuller all-in budget.
Practical process checklist (England & Wales)
- Check eligibility and lease details.
- Instruct a specialist leasehold valuer.
- Instruct a solicitor with lease extension experience.
- Decide strategy and likely offer range.
- Serve Section 42 notice (if using statutory route).
- Negotiate premium and terms.
- Complete deed of variation/new lease and register.
FAQ
Is this calculator legally binding?
No. It is an indicative planning tool only.
Can this replace a RICS valuation?
No. A specialist valuation is essential for negotiation, notice strategy, and dispute support.
Can I use it for every lease?
It works best as a high-level estimate. Complex leases, high-value properties, unusual rent review terms, and local market factors require bespoke advice.
Final thoughts
If you are considering a lease extension, speed and preparation matter. Use this calculator to sense-check costs, then get professional valuation and legal advice early—especially if your lease is approaching or below 80 years.