SDLT on Leasehold Extensions: Premium, Rent NPV, the Surcharge Trap, and Why Extension Almost Always Beats Buying Fresh

A leasehold extension is a routine event in the life cycle of a UK leasehold flat. The lease has fewer than 80 years remaining, mortgage finance becomes harder, sale becomes harder, and the leaseholder either negotiates a voluntary extension with the freeholder or invokes the statutory rights under the Leasehold Reform, Housing and Urban Development Act 1993 (with amendments legislated by the Leasehold and Freehold Reform Act 2024, only partly in force). What is less routine is the SDLT consequence: the extension is a chargeable land transaction, and a buy-to-let landlord can be surprised by an SDLT bill above the £40,000 threshold where the 5% additional dwellings surcharge bites.

This page sets out how SDLT applies to a lease extension, why it is structurally much smaller than the SDLT on a fresh purchase of the same flat, how the 2024 reforms change the statutory premium formula, and a worked comparison of the two paths. For leaseholders contemplating whether to extend now or sell and let the new buyer extend, the SDLT calculation is one (among several) inputs to the decision.

The technical mechanic: surrender and regrant

A leasehold extension under the statutory regime is legally a surrender of the existing lease and the grant of a new longer lease. For SDLT purposes the new lease is a grant of a chargeable interest under section 43 FA 2003. The buyer (the leaseholder taking the new lease) is the SDLT taxpayer. The chargeable consideration is:

• The premium paid to the freeholder for the extension. Under LRHUDA 1993 (as amended), this is calculated under the statutory formula in Schedule 13.
• The net present value of the rent payable under the new lease, calculated using the 3.5% statutory discount rate under Paragraph 3 Schedule 5 FA 2003. For statutory extensions granted at a peppercorn (nominal) rent, the NPV is effectively zero.

The surrender of the existing lease is not separately chargeable. Section 43 + Schedule 17A treat the transaction as a single grant of the new lease, not as two separate events. The deemed grant runs from the effective date (typically the completion date of the new lease deed). The 14-day SDLT return filing window runs from that effective date.

The statutory regime: LRHUDA 1993 and the 2024 reforms

Qualifying flat leaseholders can demand a statutory extension under LRHUDA 1993. The new lease adds 90 years to the existing term and reduces the ground rent to a peppercorn. The premium is calculated under Schedule 13 LRHUDA, comprising the freeholder's lost ground rent, any "marriage value" where the existing lease is under 80 years, and compensation for any diminution in value. Until the Leasehold and Freehold Reform Act 2024, a 2-year qualifying-ownership period also applied; its abolition is the one headline change already in force (January 2025).

The 2024 Act makes four headline changes, with sharply different in-force positions:

Change	Position today	LFRA 2024 position (in-force status)
Length of statutory extension	Existing term + 90 years	Fresh 990-year term (not yet in force)
Qualifying ownership period	Immediate on acquisition	2-year rule abolished (in force since January 2025)
Marriage value (uplift below 80 years)	Payable to freeholder	Abolished (not yet in force; still payable on a claim made today)
Ground rent under new lease	Peppercorn	Peppercorn (unchanged)

The marriage-value abolition is the largest practical change, and it is not yet in force. A flat with a 75-year lease (under the 80-year boundary) still attracts a substantially higher premium today because of the marriage-value component; once the abolition is commenced, the premium will be materially lower. For SDLT purposes, the practical consequence will be a smaller chargeable consideration on a statutory extension, and correspondingly smaller SDLT bills, once commencement happens. A claim made today is valued under the existing rules, marriage value included, and the HRAD threshold trap is live either way.

The 2024 Act is being commenced in phases. So far the 2-year-rule abolition (January 2025) and the Right to Manage reforms (March 2025) are in force; the 990-year term, the marriage-value abolition and the prescribed valuation rates are not, and the valuation provisions require secondary legislation (the consultation on prescribed deferment and capitalisation rates closes on 23 September 2026). The current state of commencement should be checked at the date of any extension because the position has moved several times since Royal Assent in May 2024.

The £40,000 threshold and the HRAD trap

Lease grants are notifiable for SDLT where the premium plus rent NPV is £40,000 or more. Below that threshold, no SDLT return is required and no SDLT is payable. Above it, the SDLT return is filed and the chargeable consideration runs through the standard residential bands.

The HRAD 5% additional dwellings surcharge applies on the same £40,000 threshold. Where the leaseholder owns another residential property anywhere in the world (valued at £40,000 or more), and is not replacing a main residence, HRAD adds 5% to the chargeable consideration on the extension. The effect is that a buy-to-let landlord extending the lease on one of their portfolio flats faces a surcharge that they did not pay (or that was much smaller) when they originally bought the flat.

Examples:

• Premium £30,000, owner-occupier, no other property: Below threshold. No SDLT, no return.
• Premium £30,000, BTL landlord owning 4 other flats: Below threshold. No SDLT (the £40,000 floor applies to HRAD as well as to notifiability).
• Premium £45,000, owner-occupier, no other property: SDLT on £45,000 at standard rates: £0 (under £125k nil-rate). Return required.
• Premium £45,000, BTL landlord owning 4 other flats: SDLT £0 standard, HRAD £2,250 (5% × £45k), total £2,250. Return required.
• Premium £150,000, BTL landlord owning 4 other flats: SDLT £500 standard (2% on £25k between £125k and £150k), HRAD £7,500, total £8,000.
• Premium £300,000, BTL landlord owning 4 other flats: SDLT £5,000 standard (2% on £125k + 5% on £50k), HRAD £15,000, total £20,000.

Worked comparison: extension vs fresh purchase on a £350,000 flat

Consider Priya, a buy-to-let landlord who bought a 2-bed flat in Wandsworth in 2014 for £290,000. The lease had 76 years remaining at acquisition; it now has 64 years. The flat's value with a long extended lease would be £350,000; with 64 years remaining the lease is worth around £305,000 (the 'short lease' discount). Priya is considering two paths.

Path 1: Extend the lease under the statutory regime. Premium under the current formula (including marriage value, since 64 years is below the 80-year boundary and the LFRA 2024 abolition is not yet in force; new lease = existing term plus 90 years at a peppercorn rent): estimated £42,000. SDLT consequences:

• Notifiable: yes (premium ≥ £40,000).
• Standard SDLT on £42,000: £0 (under £125k nil-rate band).
• HRAD 5% on £42,000: £2,100 (Priya owns 3 other flats).
• Total SDLT on extension: £2,100.

Path 2: Sell the existing short-leased flat and buy a fresh long-leased flat. Sale of existing flat at £305,000 (CGT triggered). Purchase of a fresh long-leased flat at £350,000. SDLT on £350,000 fresh purchase: £7,500 standard + £17,500 HRAD = £25,000. Plus estate agent fees on sale (~£4,500), legal fees on both transactions (~£3,500), removal costs if owner-occupied (not Priya), CGT on the gain (depends on base cost; assume ~£2,500 if no significant gain after acquisition costs).

Cost line	Path 1: Extension	Path 2: Sell + Re-buy
Extension premium	£42,000	,
Purchase price (new flat)	,	£350,000
Sale price (existing flat)	,	(£305,000)
SDLT	£2,100	£25,000
Estate agent + legal fees	£1,500	£8,000
CGT (estimated)	£0	£2,500
Capital outlay (net)	£45,600	£80,500

The extension path costs about £35,000 less in cash terms and leaves Priya with the same long-leased flat she would have ended up with via sale and re-purchase. The SDLT differential alone is £22,900. For most buy-to-let landlords on most flats, the SDLT mathematics overwhelmingly supports extending over selling and re-buying.

The calculus shifts in only a few situations: (a) the existing lease is so short that the freeholder is uncooperative and statutory enforcement would take 18+ months; (b) the leaseholder wants to dispose of the flat anyway for non-SDLT reasons (location, condition, rental yield); or (c) the freeholder is willing to sell the freehold to a collective enfranchisement of all the building's leaseholders, in which case the SDLT calculus changes again.

The 80-year marriage-value cliff, today and after LFRA 2024 commencement

Under the current regime the 80-year boundary matters enormously. A lease at 81 years remaining attracts a modest extension premium because the freeholder has no marriage value. A lease at 79 years remaining attracts a substantially higher premium because the freeholder gains a 50% share of the marriage value (the uplift between short-lease and long-lease values).

LFRA 2024 abolishes marriage value, but that provision is not yet in force. Once it is commenced, the 80-year cliff edge goes: premiums will change continuously with the remaining term rather than stepping up at the 80-year threshold, premiums on leases close to (and below) 80 years will typically be lower, and SDLT bills will be correspondingly lower. Until then, a leaseholder whose lease is approaching 80 years faces the same timing pressure as ever: cross the boundary before extending and the marriage-value component is added to the premium. Waiting for commencement is a gamble rather than a plan, because no commencement date has been set and the new prescribed valuation rates could move premiums either way.

Devolved tax: LBTT and LTT

Lease extensions on Scottish residential property attract Land and Buildings Transaction Tax (LBTT) rather than SDLT. The mechanic is broadly parallel under Schedule 19 LBTT(S)A 2013 (Revenue Scotland). Lease extensions on Welsh property attract Land Transaction Tax (LTT) under Schedule 5 LTTA(W)A 2017. Each devolved tax has its own rates, bands, and additional-dwelling supplements; cross-border modelling requires the devolved provision rather than read-across from SDLT.

One specific transitional question, addressed in Archer UK Ltd v Revenue Scotland, is whether a lease originally granted under SDLT (i.e. before LBTT commencement on 1 April 2015) attracts LBTT on a subsequent statutory extension. The FTT held that the transitional provisions in Schedule 19 protect the original SDLT character of the lease and no LBTT charge arises on the extension. The case is narrow but applies to a meaningful tail of Scottish leasehold flats granted pre-2015 and now being statutorily extended.

The CGT recovery point

SDLT paid on the extension is not a sunk cost from a CGT perspective. It is added to the leaseholder's allowable cost of the extension and forms part of the CGT base cost of the property going forward. On a future sale, the gain is reduced by the extension premium and by the SDLT paid on the extension. For a basic-rate residential CGT taxpayer at 18% (or 24% for higher-rate from 30 October 2024), the SDLT on the extension effectively shelters from 18% to 24% of CGT on the eventual sale. For a landlord planning a long hold, this materially softens the apparent up-front SDLT cost.

This recovery does not change the cash-flow position at extension. The SDLT is still due within 14 days of completion. It changes the long-term economics: the extension is not as expensive as the headline SDLT figure suggests, once the future CGT benefit is brought into the calculation.

Collective enfranchisement: when leaseholders buy the freehold together

An alternative to individual statutory extension is collective enfranchisement: the leaseholders of a building exercise their statutory right under Chapter 1 of LRHUDA 1993 to acquire the freehold collectively. Once the freehold is owned by a nominee company (typically a Right To Manage company or similar), each leaseholder can have their lease extended to a peppercorn 999-year term at no further SDLT cost, because the extension is granted by their own collectively-owned freeholder.

The SDLT consequence is on the freehold acquisition itself rather than on subsequent extensions. The nominee company pays SDLT on the price paid for the freehold, computed at residential rates. The price is typically substantial (a multi-flat building's freehold is rarely a small sum), so the SDLT can run into five or six figures. Once the LFRA 2024 valuation reforms are commenced, the freehold price under the new formula (no marriage value) will fall, correspondingly reducing the SDLT bill on the freehold acquisition; a claim made today is priced under the existing formula, marriage value included.

For groups of leaseholders facing materially short leases, the collective route can be cheaper across the cohort than each leaseholder paying separately for an individual extension. The SDLT calculation needs to be done on the freehold acquisition (typically by a tax adviser working with the leaseholders' enfranchisement solicitor), and the leaseholders need to model their share of the freehold cost plus their share of the SDLT against the individual-extension alternative.

Common errors leaseholders and conveyancers make

Four recurring errors we see on lease extension SDLT files.

Error 1: Treating the extension as not notifiable above £40,000. Where the premium is £40,001, the transaction is notifiable and an SDLT1 is required even though the standard rate SDLT is nil under the £125,000 band. Conveyancers occasionally miss the return, exposing the leaseholder to late-filing penalties under Schedule 55 FA 2009.

Error 2: Forgetting HRAD on a landlord's extension. A buy-to-let landlord extending the lease on one of their flats is often surprised that HRAD applies. The conveyancer assumes the extension is below the surcharge threshold because the underlying flat is not changing hands. The premium plus the HRAD piggyback above £40,000 produces the unexpected bill.

Error 3: Misapplying the NPV calculation where ground rent is retained. Voluntary extensions sometimes retain a peppercorn ground rent for a short period and then step up. The NPV calculation must use the full lease term and the contractual rent schedule, not just the initial peppercorn period. A staircased rent under a long lease can produce a non-trivial NPV.

Error 4: Not claiming sub-sale or group relief where applicable. Where the freeholder is in the same 75% corporate group as the leaseholder (rare but possible in commercial portfolios held through related entities), Schedule 7 group relief applies and the SDLT can be reduced to nil. This requires the relief to be claimed on the SDLT return; it is not automatic.

Internal links and further reading

• SDLT rates for buy-to-let and limited companies, 2026/27 , the underlying residential bands and HRAD.
• 5% SDLT surcharge refund process , for leaseholders extending one flat as part of replacing a main residence.
• Shared ownership SDLT and staircasing , parallel mechanics for an incremental SDLT charge on a leasehold flat over time.
• SDLT mixed-use property classification , the case-law landscape on the residential / non-residential boundary.
• Leasehold Reform, Housing and Urban Development Act 1993 (legislation.gov.uk) , the statutory extension regime.
• Leasehold and Freehold Reform Act 2024 (legislation.gov.uk) , the 2024 reforms.
• HMRC SDLT Manual , SDLTM12000+ on lease grants and extensions.