Lease Extension Calculator

If you own a leasehold flat, the number of years left on your lease affects its value and how easily you can sell or remortgage it. Extending the lease puts that right, but it comes at a cost, called the premium. Our Lease Extension Calculator gives you an estimate before you speak to a valuer.

Your right to extend

Most leaseholders of flats in England and Wales have a legal right to a 90-year extension with no ground rent. Since 31 January 2025, you no longer need to have owned the flat for two years before claiming. The new lease length is the years left plus 90.

How the premium is worked out

Under the current statutory method, the premium has up to three parts:

1. Loss of ground rent: the freeholder loses the ground rent for the rest of the lease. Its value is worked out using a capitalisation rate, often 6% to 7%.
2. Loss of reversion: the freeholder would have got the flat back when the lease ran out, and the extension pushes that 90 years further away. This is valued using a deferment rate, usually 5% for flats.
3. Marriage value: if the lease has less than 80 years left, the extended lease is worth more than the parts separately, and the freeholder gets half of that extra value.

That's why extending before your lease drops below 80 years usually saves a lot of money.

Changes on the way

The Leasehold and Freehold Reform Act 2024 will remove marriage value, allow 990-year extensions and set new valuation rates. At the time of writing, these parts of the Act weren't in force, so the current method still applies. Check the latest position before you serve notice.

How to use the calculator (Lease Extension Calculator)

1. Enter the flat's value with a long lease.
2. Enter the years left and the annual ground rent.
3. If you know the flat's value with its current lease, enter it. Otherwise the calculator estimates it.
4. Adjust the deferment and capitalisation rates if your valuer suggests different ones.

A worked example

With the calculator's default settings, a flat worth £300,000 with a long lease has 75 years left and a ground rent of £250 a year. The estimated premium is around £17,700, including about £6,500 for half the marriage value. With 85 years left, the estimate falls to around £8,300, because there's no marriage value.

Other costs

You'll usually pay your own solicitor and valuer, plus the freeholder's reasonable legal and valuation costs. Budget a few thousand pounds on top of the premium. Buying a flat? Our Land Registry Fee Calculator and Stamp Duty Calculator cover other costs.