LegalExplainer

What Actually Drives Lease Extension Cost

Lease extension premiums look like a black box from the outside. They are not — three variables do almost all of the work.

Ventura Research · 7 min read · Updated 20/07/2026

Key Takeaways

Lease extension premium is driven primarily by unexpired lease term, ground rent, and the deferment/capitalisation rates a valuer applies.
Premiums rise sharply — non-linearly — as unexpired term falls below 80 years, due to "marriage value".
Ground rent structure (fixed vs. escalating) has an outsized effect on premium that is often underestimated by owners.

The Three Core Inputs

A lease extension premium is built from three components: the capitalised value of the ground rent given up, the deferred value of the freeholder’s reversionary interest (the right to the property back at lease expiry), and — where the lease has fewer than 80 years remaining — a marriage value payment.

Why Sub-80-Year Leases Cost Disproportionately More

Under UK leasehold law, "marriage value" — the uplift in combined value created by merging the freehold and leasehold interests — becomes payable (typically split 50/50 with the freeholder) once unexpired term falls below 80 years. This is why premiums do not rise smoothly as lease term shortens; there is a distinct step change at the 80-year threshold, and owners are generally well advised to extend before crossing it.

Ground Rent Structure Matters More Than Owners Expect

A fixed, modest ground rent has a relatively small effect on premium. An escalating ground rent — particularly one that doubles at intervals — can be capitalised to a much larger figure, since the valuer must value the full escalating income stream the freeholder is giving up, not just the current rent.

Common Mistakes

Delaying a lease extension until after unexpired term falls below 80 years, and thereby becoming liable for marriage value that could have been avoided.
Underestimating the effect of an escalating ground rent clause on the eventual premium.
Assuming a "typical" premium from a friend’s or neighbour’s experience, without a proper professional valuation for the specific lease terms.

Professional Insight

For investors holding leasehold stock, we treat the 80-year threshold as a hard planning date, not a soft guideline — proactively extending leases before that point is one of the more reliably value-accretive, low-execution-risk actions available to a leasehold portfolio owner.

Frequently Asked Questions

Who pays for the valuation and legal costs of a lease extension?

Under the statutory process, the leaseholder is generally required to pay the freeholder’s reasonable valuation and legal costs, in addition to their own, and in addition to the premium itself.

Does extending the lease affect ground rent going forward?

Yes — a statutory lease extension typically reduces ground rent to a nominal "peppercorn" (effectively zero) for the remainder of the extended term, which is itself part of what the premium is paying for.

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