UK Lease Extension Premium Estimator
Use this free calculator to estimate the likely premium for a statutory lease extension (typically +90 years and ground rent reduced to a peppercorn).
How this lease extension calculator works
This calculator gives you a practical estimate of your lease extension premium based on common valuation components used in England and Wales. It is designed for quick planning, budgeting, and comparing scenarios before speaking with a specialist valuer or solicitor.
The estimate combines three core elements:
- Term value: compensation for future ground rent the freeholder loses.
- Reversion value: value of getting the property back later than originally expected.
- Marriage value: typically applies when the lease falls below 80 years.
Why the 80-year mark matters so much
Once your lease drops below 80 years remaining, marriage value usually becomes payable under statutory rules. That often causes extension costs to rise faster year by year. In plain terms: waiting can be expensive.
If your lease is close to 80 years, it is generally wise to get formal advice quickly. Even a small delay can affect valuation assumptions and bargaining position.
Input guide: what each field means
Current flat value with a long lease
This should be your best estimate of what the property would be worth if it had a very long lease and no onerous rent terms. Local comparables are useful here.
Annual ground rent
Use your current yearly rent. If your lease has review patterns (doubling or index-linked increases), the real premium can be higher than a simple fixed-rent model.
Years remaining
Enter exact years left on the lease now. This is one of the strongest cost drivers in any lease extension valuation.
Deferment and capitalisation rates
These rates discount future cash flows back to present value. Small changes in these assumptions can move the premium significantly, especially where many years are involved.
Relativity override
If left blank, the calculator auto-estimates relativity from years remaining. If you have surveyor evidence, you can manually enter your own relativity percentage.
What the result includes
The output gives:
- Estimated premium
- Low/high planning range
- Term, reversion, and marriage value split
- Total including your inputted professional costs
Use the range for budgeting, not as a legal offer figure. Formal notices and negotiations require expert valuation evidence.
Ways to reduce lease extension stress
- Start early: especially before the lease crosses 80 years.
- Get specialist advice: leasehold enfranchisement is niche work.
- Prepare funding: include valuation, legal costs, and potential landlord costs.
- Model scenarios: test different rates and market values before deciding your timing.
Frequently asked questions
Is this calculator suitable for all leases?
It works as a planning tool for typical flats under statutory lease extension assumptions. Complex leases, unusual rent clauses, and disputed assumptions need custom valuation.
Can I rely on this result in court or tribunal?
No. Tribunal or court submissions require professional valuation reports and supporting market evidence.
Should I extend now or wait?
If your lease is near or below 80 years, waiting often increases the cost. A valuer can model your exact position and likely premium trajectory.
Bottom line
A lease extension can protect saleability, mortgageability, and long-term value. This calculator helps you understand the likely numbers quickly so you can act sooner and negotiate from a stronger position.