If you own a leasehold flat, one of the biggest financial questions is: how much will it cost to extend my lease? This calculator gives you a fast, practical estimate based on common valuation components used in England and Wales.
How this lease extension estimate works
This tool estimates the premium by combining three core elements:
- Term value: compensation for lost ground rent income.
- Reversion value: compensation for delaying the freeholder’s right to vacant possession.
- Marriage value: if the lease is below 80 years, part of the uplift in value may be shared.
In practical terms, as lease length falls, extension cost usually rises. There is often a significant jump once the lease drops below 80 years due to marriage value.
Input guide
1) Market value with a long lease
Use an estimate of what your flat would be worth if it had a long lease (or share of freehold equivalent value). Estate agent comparables can be a starting point, but surveyor input is better.
2) Years remaining
Take this from your lease document or title information. Even a small change in remaining years can materially affect the premium.
3) Ground rent
This calculator uses a simple annual figure. Real leases can include rent review patterns, doubling clauses, and stepped rents, which can increase complexity.
4) Cap rate and deferment rate
These rates are valuation assumptions used to discount future cash flows. Typical ranges vary with market evidence and valuation practice. If you are unsure, keep the default values and treat results as broad guidance only.
5) Relativity
Relativity is the short-lease value as a percentage of long-lease value. If you leave this blank, the calculator uses an estimated curve based on remaining years. Professional valuers may use tribunal evidence and local market comparables for more accurate relativity.
Why the 80-year threshold matters
Once a lease drops below 80 years, marriage value is commonly introduced in statutory valuation. This can make the premium notably higher than if the extension is started earlier. Many leaseholders aim to act before crossing this line.
Worked example (conceptual)
Imagine a flat worth £350,000 on a long lease, with 72 years remaining and £250 annual ground rent. The calculator will estimate:
- Present value of future rent loss
- Present value of delayed reversion
- Potential marriage value (because 72 is below 80)
The total gives an estimated premium range. Negotiations, evidence, legal drafting, and professional reports may push the final figure up or down.
Important costs beyond the premium
Even if you estimate the premium correctly, budget for:
- Your valuer’s fee
- Your solicitor’s fee
- Freeholder’s reasonable valuation and legal fees (where applicable)
- Land Registry and potential notice fees
Final note
This leasehold extension calculator is designed to help you sense-check affordability and timing. For a binding figure, use a qualified leasehold valuer and solicitor with local experience in lease extension work.