Leasehold Calculator

Estimate your lease extension premium

Use the calculator below to estimate the premium for extending your lease under the Leasehold Reform, Housing and Urban Development Act 1993 — the statutory route that adds 90 years to your lease and reduces the ground rent to a peppercorn (nil). Enter your property's value, the unexpired term and your annual ground rent, and it returns an indicative premium range with a full breakdown of how the figure is built up.

Two numbers matter most. The unexpired term drives everything: once a lease falls below 80 years, marriage value applies and the premium rises sharply — which is why acting before the 80-year threshold is the single best piece of leasehold advice there is. And the ground rent: fixed modest rents add little, but escalating or doubling rents can add substantially more than this calculator shows, so take advice if your lease contains rent reviews.

How is a lease extension premium calculated?

The statutory premium the calculator estimates is built from three components, and the breakdown shows each one:

• Ground rent compensation (the “term”) — the freeholder loses your ground rent for the rest of the current lease, so the premium includes those payments converted into a single capital sum today.
• The reversion — the freeholder was due to get the flat back at the end of the lease; a 90-year extension pushes that day 90 years further away, and the premium compensates for the wait. The longer your remaining lease, the smaller this component.
• Marriage value — added only where the unexpired term is below 80 years (see below).

In a real claim each input is argued on evidence — the flat's value, relativity, and the deferment and capitalisation rates — which is why the calculator returns a range rather than a single figure.

What is marriage value — and why does 80 years matter?

Extending a short lease creates value: the extended flat is worth more than the short-lease flat and the freeholder's interest combined were before. That uplift is called marriage value, and under the statutory valuation regime currently in force the freeholder is entitled to half of it once the lease has fallen below 80 years. Try the calculator at 82 years and again at 78 to see the effect — the jump is the 80-year rule in action. Reform legislation is expected to change how premiums are calculated, but the changes are being phased in; claims valued today follow the current rules.

What the calculator can't see

An online estimate works from three inputs; a formal valuation works from the lease and the market. Escalating or doubling ground rents, an intermediate (head) lease, unusual lease terms, flat-specific condition and genuine local comparable evidence can all move the premium materially — usually in ways only an inspection and a read of the lease reveal. Treat the result as a budgeting tool, not a negotiating position: the freeholder will almost always open higher.

From estimate to formal valuation

The result is an indicative estimate, not a valuation — real premiums are negotiated on relativity evidence and settled figures. When you are ready to proceed, our panel's lease extension surveyors provide the formal RICS valuation, serve the section 42 notice figures and negotiate on your behalf — and if agreement can't be reached, the same panel provides expert evidence at the First-tier Tribunal. If your whole building is thinking bigger, compare the numbers against collective enfranchisement. You can cross-check results against the Leasehold Advisory Service calculator.