Off-Plan Property & Stamp Duty
How stamp duty works for off-plan property purchases. SDLT is not triggered at legal completion — it is triggered by "substantial performance," which can happen months earlier. Understanding this distinction is critical to avoiding penalties, rate surprises, and missed deadlines.
In this article
Key Takeaways
- Off-plan SDLT is triggered by "substantial performance" — NOT legal completion. This catches many buyers off guard
- Substantial performance occurs when you take possession of the property OR pay 90% or more of the purchase price — whichever happens first
- SDLT must be filed and paid within 14 days of substantial performance (HMRC guidance SDLTM07700)
- Taking possession includes any access: moving in, receiving keys, snagging visits where you control access
- If SDLT rates change between exchange and substantial performance, the rate at substantial performance applies — rate change risk is real
- Staged payment plans that exceed 90% of the price before legal completion trigger SDLT at the 90% payment point
- First-time buyer relief is assessed at the date of substantial performance — if thresholds change during the build period, the new thresholds apply
Critical: SDLT is due when you take possession — not at completion
The single most important thing to understand about off-plan SDLT is that the 14-day filing clock starts ticking when you take possession or pay 90% of the price — not when legal completion occurs. Many off-plan buyers miss this and face penalties. If you receive keys before legal completion for any reason, SDLT is due within 14 days.
How Off-Plan Purchases Work
Buying off-plan means exchanging contracts on a property that does not yet exist — or exists only in part — before legal completion. The typical off-plan timeline:
Stage 1: Exchange of contracts
You pay a deposit (typically 10%) and commit to buying the property on the agreed terms. The developer builds the property. The SDLT clock does not start here.
Stage 2: Construction period
The developer builds. Depending on the scheme, you may make staged payments. The build period can be 6–24+ months for larger developments. No SDLT during this period unless a trigger event occurs.
Stage 3: Substantial performance (SDLT trigger)
SDLT is triggered here — at the earlier of: taking possession or paying 90% of the price. The 14-day filing deadline starts from this date.
Stage 4: Legal completion
Legal title transfers. If SDLT was already paid at substantial performance, no further SDLT is due on completion (though a further return may be required to notify HMRC).
Use our stamp duty calculator to check the SDLT on your off-plan purchase, and see our residential property stamp duty guide for the standard rate schedule that applies to most off-plan homes. Also see our building plot guide if purchasing land off-plan for a self-build.
Substantial Performance Rules
"Substantial performance" is an HMRC concept defined in Finance Act 2003. HMRC's SDLT Manual at SDLTM07700 explains these rules in detail. In summary, a contract is substantially performed when:
Trigger 1: Taking possession
You take possession of the property — meaning you have the right to occupy, use, or control it. This includes:
- Moving furniture into the property
- Receiving keys from the developer
- Carrying out snagging visits where you control access
- Using the property for storage
- Any "early key release" arrangement
Trigger 2: Paying 90% of consideration
You have paid 90% or more of the total purchase price. This occurs when:
- Staged payments during construction reach 90% of the price
- The exchange deposit plus interim payments total 90%+
- A single pre-completion payment takes you over 90%
Earlier event always wins
If you receive keys 3 months before legal completion AND staged payments reach 90% 6 months before completion, the key receipt (3 months before) is the earlier event — and that is when SDLT is triggered. HMRC takes the earlier of the two triggers in all cases.
When SDLT Is Due
The off-plan SDLT timeline differs from a standard purchase. Understanding the effective date is critical:
| Event | Standard Purchase | Off-Plan Purchase |
|---|---|---|
| Exchange of contracts | Not an SDLT event | Not an SDLT event |
| Taking possession | Usually same as completion | SDLT trigger — 14 days to file |
| Paying 90% of price | N/A | SDLT trigger if before possession |
| Legal completion | SDLT trigger — 14 days to file | May be after SDLT already paid |
Where SDLT is paid at substantial performance, a further SDLT return (but no additional payment) may be required at legal completion to confirm the transaction details. Your solicitor will handle this.
The 14-Day Filing Deadline
Once substantial performance occurs, you have exactly 14 calendar days to file the SDLT return (SDLT1) and pay the tax. This is not a working day deadline — it includes weekends and public holidays.
Penalties for late filing
1 day late: £100 automatic penalty
3 months late: Additional £200 penalty
12 months late: HMRC may charge a tax-geared penalty (up to 100% of the tax due)
Interest: Charged on overdue SDLT from day 15 until payment date
The practical risk for off-plan buyers is receiving keys for snagging or early access without realising this starts the 14-day clock. Always confirm with your solicitor whether any key release arrangement constitutes "taking possession" for SDLT purposes before accepting keys.
Your solicitor's responsibility
In a standard property purchase, your solicitor files the SDLT return at completion. For off-plan properties, brief your solicitor explicitly about any early key release, snagging access, or staged payment arrangements. They need to monitor all potential substantial performance triggers — not just the legal completion date.
Rate Changes Between Exchange and Completion
Off-plan purchases with long build periods carry a unique SDLT risk: rate changes. The SDLT rate that applies is the rate in force at the date of substantial performance, not the rate at exchange. If rates increase during the build period, you pay the higher rate.
Example: rate change risk
January 2024: You exchange on a £400,000 off-plan flat. SDLT at standard residential rates would be £7,500. You pay a 10% deposit (£40,000).
April 2025: SDLT rates change — the nil-rate threshold drops from £250,000 to £125,000.
June 2025: You take possession and substantial performance occurs.
SDLT due is calculated at the April 2025 rates, not the January 2024 rates when you exchanged.
This equally applies to rate reductions
The reverse is also true — if SDLT rates fall during your build period, you benefit from the lower rates at substantial performance. The rate at the trigger date is what counts, whether higher or lower.
First-time buyer threshold changes
First-time buyer relief thresholds also apply at the date of substantial performance. If you exchange when the FTB nil-rate is £300,000 but thresholds change before you take possession, the threshold at substantial performance governs your relief. This can work for or against you depending on the direction of change.
Deposit Structure and SDLT Timing
The structure of your deposit and payment schedule can inadvertently trigger substantial performance before you expect it.
Standard 10% deposit structure
Exchange: 10% deposit → balance (90%) paid at legal completion. Substantial performance occurs at possession or completion — whichever is earlier. No 90% payment trigger fires during the construction period.
Staged payment plan — 90% trigger risk
Exchange: 10% → 20% at foundations → 30% at watertight stage → 30% at practical completion → 10% at legal completion. Payments reach 90% at "practical completion" — before legal completion. The 90% trigger fires here. SDLT is due within 14 days of that payment.
Track your cumulative payments carefully
If your purchase has any staged payment arrangement, track the cumulative total. The moment it reaches or exceeds 90% of the total price, substantial performance is triggered. Alert your solicitor immediately when you make a payment that may reach the 90% threshold.
Scotland and Wales Equivalents
Substantial performance rules apply in Scotland and Wales under their respective land transaction taxes.
Scotland — LBTT
LBTT has equivalent substantial performance provisions. The "effective date" rules under Revenue Scotland guidance mirror the SDLTM07700 principles. The 30-day filing deadline under LBTT provides slightly more time than England's 14-day deadline after substantial performance.
Wales — LTT
Wales LTT applies the same substantial performance principles under the Land Transaction Tax Act 2017. The Welsh Revenue Authority (WRA) administers LTT. Wales also has a 30-day filing deadline from substantial performance — longer than England's 14-day window.
Practical Tips for Off-Plan Buyers
1. Brief your solicitor on all key release arrangements before agreeing to them
Never accept early keys without first confirming the SDLT implications with your solicitor. What feels like a routine snagging visit can trigger a 14-day SDLT deadline.
2. Track cumulative payments against the 90% threshold
If you have a staged payment schedule, maintain a running total. Alert your solicitor the moment you approach 90% of the total price so they can prepare the SDLT return in advance.
3. Monitor SDLT rate change announcements during the build period
Budget statements, Autumn Statements, and emergency fiscal events can change SDLT rates. Ask your solicitor to flag any changes that could affect your upcoming substantial performance date.
4. Confirm your substantial performance date with your solicitor in writing
After any potential trigger event (key receipt, large payment), ask your solicitor to formally confirm whether substantial performance has occurred and what the filing deadline is. Do not assume — confirm in writing.
5. Budget SDLT funds from the point of substantial performance, not completion
SDLT on an off-plan purchase may need to be funded before legal completion — potentially before you draw down your mortgage. Ensure you have the SDLT amount available as cash from the point of substantial performance.
HMRC reference: SDLTM07700
HMRC's SDLT Manual at SDLTM07700 ("Substantial performance: contract substantially performed") is the authoritative guidance on when SDLT becomes due for off-plan contracts. Your solicitor should be familiar with this guidance. If you are dealing directly with HMRC on an enquiry, reference SDLTM07700 to ensure the correct provisions are applied.
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Emma Richardson, MRICS
Chartered Surveyor & Property Tax Specialist
Emma Richardson is a RICS-qualified Chartered Surveyor with over 12 years of experience in UK property taxation. She founded Stamp Duty Calculator to help buyers understand the complex world of property transaction taxes.