What Happens Between Exchange and Completion on a UK New Build? Overseas Buyer Guide 2026

What Exchange and Completion Actually Mean

When you buy a UK new-build property, the transaction splits into two legally distinct events. At exchange of contracts, you and the developer sign identical copies of the contract — a moment that makes the agreement legally binding on both sides. A deposit, typically 10% of the purchase price, is paid and held by the developer’s solicitor until completion. From this point, neither party can walk away without serious financial consequences: you risk forfeiting your deposit; the developer faces penalty compensation.

Completion is the second event: the day legal ownership transfers to you. Your solicitor transfers the remaining purchase balance, the title deed registers in your name at HM Land Registry, and you receive the keys. For a standard resale property, exchange and completion can be as little as one to four weeks apart. For a new-build bought off-plan, the gap is routinely six to eighteen months — because the property may still be under construction. Everything that happens in that interval is what this guide covers.

IREIS Properties advises every client buying a UK new-build to understand the exchange-to-completion period in detail before signing the reservation form — because it is during this window that most of the practical planning must happen.

For a comprehensive overview of the full purchase process, see our complete UK new-build buying guide.

The Completion on Notice Clause — What Overseas Buyers Must Plan For

Unlike a resale transaction, where both parties agree a fixed completion date at exchange, off-plan new builds almost universally include a completion on notice clause. This gives the developer the right to serve a formal notice once the property reaches a specified stage of readiness, after which the buyer typically has 10 working days to complete.

For overseas buyers, this has a direct practical implication: you cannot arrange your international bank transfer, your travel to the UK, or your power of attorney around a fixed calendar date set months in advance. Instead, you must maintain readiness throughout the developer’s estimated completion window — usually described in the contract as a quarter, such as Q1 2027.

Reputable developers will provide construction progress updates as completion approaches, narrowing the window to a few weeks. Your solicitor should confirm that the contract contains reasonable protections if the developer materially delays the completion notice beyond the agreed quarter without justified cause. If the notice is delayed beyond a specified number of weeks, you may be entitled to rescind and recover your deposit — but this right must be expressly written into the contract.

Your Mortgage Offer: Managing Validity Between Exchange and Completion

This is where the extended exchange-to-completion gap creates the most direct financial risk for buyers. A standard UK residential mortgage offer is valid for six months from the date of issue. For a new-build bought off-plan, completion may be twelve or even eighteen months away — well beyond this window.

Most specialist new-build mortgage lenders now offer initial validity periods of nine to twelve months, with a formal extension process available if construction overruns. However, extensions are not automatic. The lender will reassess your income, credit file, and the current valuation of the property before agreeing. If your circumstances have changed — or if market values in that location have shifted since the original valuation — the lender may revise the offer terms or decline to extend.

IREIS Properties recommends working with a mortgage broker experienced specifically in new-build transactions, who understands which lenders have the strongest track record for extensions and which handle overseas clients effectively. Select the longest initial offer period available from a suitable lender, rather than simply accepting the first offer. Prepare your income documentation for a possible reassessment six to eight months after exchange, rather than being surprised by the requirement at a critical moment.

Building Insurance: Who Covers the Property During the Gap?

In a standard resale transaction, risk passes to the buyer at exchange of contracts — under the Standard Conditions of Sale in England and Wales, this means you take on responsibility for arranging buildings insurance from exchange day onwards.

For new builds, the position is typically different. Because the structure is still under the developer’s control at exchange — and in many cases still under construction — the developer’s site insurance usually remains in force until legal completion. You should not assume this, however: confirm with your solicitor that the developer’s insurance covers the property between exchange and completion, and check the contract for any clause that transfers risk to you at an earlier point.

From completion day, buildings insurance is your responsibility — and most mortgage lenders will require evidence of a valid policy before releasing funds on completion day. Arrange your buildings insurance in advance and have the confirmation document ready to send to your solicitor and lender.

The Snagging Survey — Your Right Before Keys Are Handed Over

A snagging survey is a professional inspection of the finished property designed to identify defects before you legally complete. These range from cosmetic issues — paint splashes, scratched tiles, misaligned doors — to more significant matters such as incomplete plumbing, improperly fitted windows, or defective electrical work.

Under the New Homes Quality Code, registered developers are required to allow buyers access for a professional pre-completion snagging inspection. The survey results are presented to the developer, who is expected to rectify defects before completion or commit in writing to do so within a defined period under the property warranty — typically a 10-year NHBC Buildmark warranty or an equivalent scheme.

Practical steps for overseas buyers:

• Book your snagging surveyor early. Once the developer confirms a practical completion date, reputable snagging specialists fill quickly. Allow four to six weeks of lead time.
• Get written commitment on remediation. Ensure your solicitor secures written confirmation listing any defects to be rectified and the timeline for doing so.
• Do not complete with unresolved safety defects. If significant structural or safety issues remain, take legal advice before proceeding. Your solicitor should advise on your right to withhold completion in extreme cases.

When Is Stamp Duty Land Tax Due?

One of the most frequently misunderstood aspects of the exchange-to-completion period is the timing of Stamp Duty Land Tax (SDLT). The tax trigger is the completion date, not the exchange date. According to HMRC, buyers must submit an SDLT return and pay any tax due within 14 days of the effective date of the transaction — for a new-build purchase, that is the completion day itself.

Your conveyancing solicitor handles both the return and the payment on the day of completion, drawing the funds from your completion monies. This means that during the entire exchange-to-completion period, your SDLT liability has not yet crystallised in terms of timing — but you should understand the amount well in advance.

For overseas buyers, the SDLT calculation includes the standard tiered rates, the 2% surcharge for non-UK residents, and — if you already own another residential property anywhere in the world — the higher rate for additional dwellings. Because these surcharges layer on top of one another, the total can be materially higher than the basic rate alone. Use the IREIS Properties stamp duty calculator to model your precise figure based on your residency status, purchase price, and existing property ownership — before you exchange, not the morning of completion.

For a full breakdown of UK property purchase costs and taxes, see our costs and taxes overview.

Practical Checklist for Overseas Buyers Before Completion

The following steps apply specifically to buyers who are not physically based in the UK.

Three to four months before expected completion:

• Confirm your mortgage offer is valid beyond the expected completion window, or initiate a lender extension request.
• Book your snagging surveyor.
• Confirm your solicitor holds current, valid proof of your identity and address — AML re-verification is required at completion if original checks were conducted more than 12 months earlier.
• Review the completion notice clause in your contract with your solicitor and understand the notice period.

Six to eight weeks before:

• Arrange your international wire transfer with a specialist FX broker. For transfers of this size, consider a forward contract to lock in the exchange rate ahead of completion. Taiwanese buyers should consult a specialist FX broker to monitor the NTD/GBP rate and, where possible, lock in a forward contract ahead of completion.
• Confirm your buildings insurance start date aligns with your expected completion day.
• If you will not be present in the UK on completion day, ensure your solicitor holds a valid power of attorney to act on your behalf.

Completion day:

• Your solicitor transfers the balance and receives confirmation of title registration from HM Land Registry.
• SDLT is filed and paid on the same day.
• Keys are released once the developer’s solicitor confirms receipt of funds in cleared form.

For the complete picture of the UK new-build buying journey from reservation to handover, the IREIS Properties team is available to guide you through every step — visit our UK property buying process guide or explore our full buying guides resource centre.