Buying a house at auction: Your 28-day completion survival guide

When the hammer falls at a traditional property auction, you have exchanged contracts. There is no cooling off period, no renegotiation after the survey, and no polite withdrawal if your mortgage falls through. You pay a 10% deposit on the day and you are contractually bound to complete, usually within 28 days. That speed is exactly why auctions attract buyers, and exactly why they punish the unprepared.

This guide walks through the whole 28-day sprint, from the work you must do before you ever raise a hand to the day the keys become yours.

Before the auction: The work that decides everything

The single biggest difference between auction and ordinary purchase is that all the due diligence happens before you bid, not after. Once the hammer falls you own the problems as well as the property.

Three jobs matter most:

1. View the property and commission a survey if the numbers justify it. Auction stock leans heavily towards properties with issues, which is why it is cheap.
2. Have a solicitor review the legal pack, the bundle of title documents, searches and contract conditions the seller publishes before the sale. We cover this in detail in our separate article on auction legal packs, but the short version is that bidding without a professional review is how buyers end up owning unsellable titles and someone else's legal bills.
3. Sort your finance completely, because 28 days is not long enough to start a mortgage application from scratch. Set your maximum bid with every cost included: the hammer price is only part of what you will pay once conveyancing fees, stamp duty and any works are counted, and the discipline to stop bidding at your number is the cheapest protection the room offers.

Money: Deposit, fees and finance

On auction day you need the 10% deposit available immediately, plus the auction house administration fee, which commonly runs from a few hundred pounds to over a thousand. Check the catalogue and the special conditions carefully: some lots also oblige the buyer to pay the seller's legal costs or a buyer's premium on top of the hammer price.

For the remaining 90% you have three realistic routes:

• Cash, the simplest and the reason cash buyers dominate auction rooms.

• A mortgage arranged in advance, with the valuation booked before auction day. A standard application started after the auction will rarely complete in 28 days, so you need a lender and broker who understand auction deadlines, with an agreement in principle and, ideally, the valuation already done.
• Bridging finance, which is fast and flexible but expensive. Many auction buyers bridge first, then refinance onto a mortgage afterwards. Industry data suggests roughly a third of auction purchases involve bridging at some stage.

Whatever the route, stress test it. If you fail to complete, you lose your 10% deposit and can be sued for the seller's losses on a resale. That is not a theoretical risk; it is the standard remedy in auction conditions.

The hammer falls: What happens legally

At a traditional, unconditional auction, the fall of the hammer is exchange of contracts. You sign the memorandum of sale, pay the deposit and the property is yours to complete. Risk usually passes to you at that moment too, so buildings insurance must start on auction day, not on completion day.

One deadline that surprises first timers: Stamp Duty. An SDLT return must be filed and any tax paid within 14 days of completion, and if the auction property is an additional dwelling for you, the 5 per cent surcharge applies. The rules and current bands are on the government's stamp duty pages.

The 28 days: Week-by-week

Week one belongs to instruction and mobilisation. Your solicitor receives the contract from the auctioneer, checks the legal pack against what you were told on the day, raises any genuinely urgent enquiries, and gets your identity and source of funds verification done. If you are borrowing, your lender or bridging provider instructs its valuation immediately if it has not already happened.

Week two is finance week. The mortgage offer or bridging facility must be issued, the lender's legal requirements dealt with, and any search gaps covered. Auction sellers often provide searches in the pack; where they are missing or stale, buyers usually rely on search indemnity insurance rather than waiting weeks for new results.

Week three is for the mechanics: signing the mortgage deed, receiving the completion statement, transferring your balance to the solicitor in good time. Bank transfer limits catch people out here, so warn your bank early.

Week four is completion. Your solicitor sends the balance, the seller's solicitor confirms receipt, and the keys are released. Miss the date and the auction conditions typically charge penal interest for every day of delay, on top of putting your deposit at risk if you never complete at all.

Conditional auctions work differently

The modern method of auction, common online, is conditional: the hammer buys you an exclusivity period, usually 56 days, in exchange for a non-refundable reservation fee that often runs to several per cent of the price. You are not exchanging contracts on the day, which softens the deadline but adds a significant fee that does not count towards the purchase price. Read which type of auction you are in before you bid, because the two carry very different risks.

The bottom line

Auction buying rewards preparation and punishes optimism. Do the legal work before the sale, have every pound of funding proven before you bid, insure from the day of the hammer, and treat the 28 days as a project plan rather than a countdown. A conveyancer who regularly handles auction purchases is not optional here; comparing specialist conveyancing quotes before auction day means your solicitor starts running the moment the hammer falls.