Lease Extension Cost Estimator
Estimate the premium you might pay to extend your lease — and understand whether marriage value applies to your situation.
Your lease details
Under 80 years — marriage value applies
Ground rent affects the premium calculation. After a statutory extension under the 1993 Act, this reduces to a peppercorn (£0).
Estimated extension premium
Rough ranges only — not a valuation
Leasehold & Freehold Reform Act 2024
The Leasehold and Freehold Reform Act 2024 will abolish marriage value and standardise 990-year extensions when it comes into force. As of April 2026, these provisions are not yet active.
Lease extension — what you need to know
Under the Leasehold Reform, Housing and Urban Development Act 1993, most flat owners have a statutory right to extend their lease by 90 years at a peppercorn (zero) ground rent — provided they have owned the property for at least two years.
The premium is calculated using a complex formula that accounts for the ground rent being capitalised, the reversion value (what the freeholder gets back when the lease expires), and — where the lease is under 80 years — marriage value.
Marriage value is the increase in the property’s market value that the extension creates. Under the 1993 Act, 50% of this uplift must be paid to the freeholder. This is why letting a lease fall below 80 years is one of the costliest mistakes a leaseholder can make.
Always instruct a RICS-accredited leasehold valuer before serving a Section 42 notice — an incorrect premium can leave you exposed in tribunal proceedings.
Key thresholds
- Below 80 yearsMarriage value applies
- Below 70 yearsMortgage risk begins
- Below 60 yearsHard to mortgage
- Below 50 yearsLargely unmortgageable
- Post-extension+90 years added
- New ground rentPeppercorn (£0)