When SDLT falls due: substantial performance vs completion
For most of the 763,112 residential sales recorded across England and Wales in 2025 (HM Land Registry price-paid data, file dated 31 December 2025), stamp duty is a completion-day event: contracts exchange, money and keys move on the same day, and the buyer's conveyancer files the return shortly after. But the tax point — the "effective date" that fixes both the filing deadline and which rate table applies — is not always completion. A rule called substantial performance can pull it forward, sometimes by months.
This matters because the effective date does three things at once: it starts the 14-day clock for the stamp duty return, it fixes the rates and reliefs that apply, and it sets the buyer's circumstances (first home, additional property, and so on) that the tax is judged against. Get the date wrong and a return can be late before anyone realises the clock has started.
This is a general explanation of how the rules work, not advice on any particular purchase. A conveyancer or tax adviser confirms the effective date for a specific transaction.
The default: completion is the effective date
Section 119 of the Finance Act 2003 sets the starting point. The "effective date" of a land transaction is the date of completion — the day the purchase deed is executed and the price is paid. For a straightforward buy-and-move-in-on-the-same-day purchase, that is the end of the story.
The default matters because everything downstream keys off it. How a property's status is judged at the effective date explains how the physical state of a property on that single day — not the plans or the brochure — decides whether residential or non-residential rates apply. The date, in other words, is the hinge for the whole calculation.
The exception: substantial performance (s44 FA 2003)
Section 44 of the same Act carves out an important exception. Where a contract is to be completed by a later conveyance, and the buyer substantially performs the contract before that completion, the effective date is brought forward to the date of substantial performance.
A contract is treated as substantially performed the moment either of two things happens — whichever comes first:
| Test | What triggers it |
|---|---|
| Possession | The buyer takes possession of the whole, or substantially the whole, of the property — moving in, taking a licence to occupy, starting renovation works, or becoming entitled to the rents and profits (s44(5)–(6)). |
| Payment | The buyer pays a substantial amount of the consideration. HMRC's SDLT Manual treats "substantial" as around 90% of the total price (SDLTM07850 onwards). |
Only one of the two needs to be met. A buyer who moves in early has substantially performed on the possession limb even if not a penny of the price has changed hands; a buyer who pays 90% up front has done so on the payment limb even if they never set foot inside.
Why this reaches ordinary buyers, not just developers
Substantial performance is often thought of as a developer's problem — staged payments, off-plan purchases, options. But three everyday situations trip the possession limb:
- Early access to renovate. A buyer allowed in before completion to start works — stripping a kitchen, replastering — has taken possession. The effective date moves to the day works began.
- Moving in early on a licence. Where a seller lets a buyer occupy ahead of completion (a delayed chain, a rented-back arrangement), that occupation is possession.
- Long delayed completions with staged payments. A purchase that dribbles the price out over months can cross the ~90% payment threshold well before the deed is signed.
In each case the tax point is the earlier date. The 763,112 sales logged in 2025 sat at a median of £295,000 (HM Land Registry) — the great majority are ordinary owner-occupier purchases, and any of them can meet the possession test if the buyer gets the keys early.
The 14-day clock starts at the effective date
Section 76 FA 2003 requires the land transaction return to be filed — and the tax paid — within 14 days of the effective date. (The window was cut from 30 days to 14 with effect from 1 March 2019.)
Read together with s44, the consequence is concrete. Consider a £300,000 purchase — just above the 2025 median — where the buyer takes the keys and starts works three months before completion:
| Event | Timing | What happens |
|---|---|---|
| Buyer takes possession, starts works | Day 0 | Substantial performance — the effective date |
| Return and payment due | Day 14 | The s76 deadline runs from possession, not completion |
| Legal completion | ~Day 90 | Later conveyance; no second charge (see below) |
The return is due 14 days after possession. A buyer — or conveyancer — who assumes the clock starts at completion could be almost three months late. A related snare, where a return falls due even though no tax is payable, is covered in the £40,000 return-filing trap.
The rate table is frozen at the effective date
Because the effective date fixes which rules apply, moving it can change the bill when thresholds shift between substantial performance and completion. The clearest recent example is the 1 April 2025 reversion, when England's nil-rate band dropped from £250,000 back to £125,000 and first-time buyer relief tightened. What changed for stamp duty since April 2025 sets out the full before-and-after.
A £300,000 standard purchase illustrates the swing. Using the current (post-1-April-2025) England residential rates — 0% up to £125,000, 2% on £125,001–£250,000, 5% on £250,001–£925,000 — the sums are:
| Buyer type | SDLT on £300,000 (current rates) |
|---|---|
| Standard (home mover) | £5,000 |
| First-time buyer (nil up to £300,000) | £0 |
| Additional property (+5% surcharge) | £20,000 |
Now the timing point: a standard buyer whose contract was substantially performed on, say, 20 March 2025 — keys taken early — is taxed under the pre-reversion table (the nil-rate band was then £250,000), where the same £300,000 attracted £2,500 — even if legal completion slipped into May. The effective date, not the completion date, decides which table governs. That is a description of how the transitional rule works, not a suggestion to time a purchase around it — which table applies is a question of fact for a conveyancer.
What substantial performance does not do
Two limits are worth stating plainly, because the rule sounds more alarming than it is:
- It does not double the tax. Where a contract is substantially performed and then later completed, both events are technically notifiable, but s44 stops the tax being charged twice — the later completion is set against what was already paid, and a further return is needed only if the consideration has increased.
- It does not change the ordinary case. For the everyday same-day exchange-and-complete purchase, substantial performance and completion are the same day. The rule only bites where possession or payment runs ahead of the deed.
The bottom line
Stamp duty crystallises on the effective date, and the effective date is completion — unless the buyer takes possession or pays substantially the whole price first, in which case it jumps forward to that earlier moment (FA 2003 s44 and s119). That earlier date starts the 14-day filing clock (s76) and freezes the rate table and reliefs. For most buyers the two dates coincide; for anyone getting early access to renovate, moving in ahead of completion, or paying in stages, they may not.
You can see the all-in cost of any property — mortgage at today's Bank of England quoted rate, council tax, energy and stamp duty for a given situation — by searching a postcode on Homecost, or model the duty directly with the stamp duty calculator. For more on how the tax is structured, browse the Cost Intelligence guides.
This is general information about how the rules work, not tax or legal advice. The effective date and the tax due on any specific purchase depend on its facts. Speak to a qualified adviser before acting.
Based on 763,112 HM Land Registry residential transactions in England and Wales in 2025 (file dated 31 December 2025).