Extending a flat's lease gets more expensive the shorter it gets — especially once it drops below 80 years. Enter your flat's value, the years remaining and the ground rent to estimate the premium plus the legal and valuation fees on both sides.
Premium + fees · 2026 guide
When you extend a flat's lease, you pay the freeholder a premium. It is made up of a few elements: compensation for the ground rent the freeholder gives up, compensation for getting the flat back later (the reversion), and — if the lease is under 80 years — a share of the marriage value. The shorter the lease and the higher the ground rent, the larger the premium.
Beyond the premium you normally pay several sets of fees:
This tool gives a rough guide so you can budget. Lease valuation is a specialist area, so always commission a formal valuation before serving a Section 42 notice. For the wider cost of owning a leasehold flat, see the service charge calculator and conveyancing cost calculator.
It varies hugely with the flat's value, the years left and the ground rent. A lease with plenty of years remaining might cost a few thousand pounds, while a short lease under 80 years can cost tens of thousands because of marriage value. On top of the premium you pay your own and the freeholder's reasonable legal and valuation fees.
Marriage value is the extra value created by extending the lease, which the law currently splits 50/50 between you and the freeholder once the lease falls below 80 years. It can add many thousands of pounds to the premium, which is why people are advised to extend before the lease drops below 80 years.
Below 80 years remaining, marriage value becomes payable, sharply increasing the premium. Above 80 years it does not apply, so the cost is much lower and more predictable. If your lease is approaching 80 years, extending sooner usually saves a significant amount.
Under the current statutory route, yes — you normally pay your own legal and valuation fees and the freeholder's reasonable legal and valuation costs as well. This calculator includes a rough allowance for both sides, but a surveyor's formal valuation is essential before you serve notice.
