The 28 day clock starts when the hammer falls
At a traditional auction, the fall of the hammer is an exchange of contracts. The buyer normally pays a 10% deposit on the day and signs a contract that requires completion within a fixed period, most commonly 28 days. Some auction houses use 14 or 20 working days, and modern method auctions often allow 56 days. Miss the deadline and the seller can serve notice, charge penalty interest and ultimately keep the deposit.
That deadline is the reason this question exists. If completion had no time limit, a mortgage would almost always be the cheaper route. With a hard deadline, the question becomes which product can actually complete in time.
Why a mortgage often cannot complete in 28 days
A buy to let mortgage application typically takes four to eight weeks to reach a formal offer. Valuation booking, underwriting queues and any request for further documents all sit inside that window, and the legal work runs after or alongside it. A well prepared case with a decision in principle, a mainstream property and a responsive solicitor can complete inside 28 days, but there is little room for anything to slip.
The property itself is often the bigger problem. Auction lots are frequently there because they do not suit mortgage lenders: no kitchen or bathroom, structural issues, short leases, non-standard construction or sitting tenants on unusual terms. A mortgage valuer who deems a property uninhabitable will usually trigger a decline or a retention, and the 28 days are gone.
Why bridging fits the deadline
Bridging lenders underwrite the asset and the exit rather than rental income, and most can move from application to completion in one to three weeks. Many will lend on properties that are not currently mortgageable, on the basis that the buyer will refurbish and then sell or refinance. The trade off is cost: monthly interest of roughly 0.75% to 1.1% plus an arrangement fee of about 2%, against a mortgage pay rate that is a fraction of that.
A worked example at £180,000
Take a lot that sells for £180,000 with 28 day completion.
| Item | Figure |
|---|---|
| Purchase price | £180,000 |
| Deposit paid on auction day (10%) | £18,000 |
| Balance due within 28 days | £162,000 |
| Bridging loan at 70% of purchase price | £126,000 |
| Further buyer funds needed to complete | £36,000 plus fees |
The buyer's £18,000 deposit plus a further £36,000 covers the £54,000 gap between the £126,000 loan and the £180,000 price. If the bridge runs for six months at 0.9% a month, interest is £126,000 x 0.009 x 6 = £6,804, and a 2% arrangement fee adds £2,520. You can test your own figures on our bridging cost calculator, and the full fee breakdown is on our guide to what a bridging loan actually costs.
When a mortgage can still work
Mortgages do complete auction purchases. The cases that succeed tend to share the same features: a decision in principle before auction day, a habitable property of standard construction, a lender known for fast processing, a solicitor instructed before the auction, and ideally a 56 day modern method timescale rather than 28 days. Some buyers also negotiate a longer completion with the seller before bidding.
What usually decides marginal cases
Three things tend to settle it. First, the condition of the property: anything a valuer could call uninhabitable points to bridging. Second, the timescale in the legal pack: 28 days points to bridging, 56 days keeps a mortgage in play. Third, the exit: a bridge is only as good as the plan for repaying it, whether that is a sale or a remortgage once works are done, which we cover in our guide to exiting a bridging loan. Lenders will want that exit evidenced before they lend, not after.
What slows auction cases down is rarely the lender. It is usually the legal pack: missing searches, unusual covenants, short leases or seller solicitors who are slow to answer enquiries. Reading the legal pack before bidding, and having a broker line up the finance before auction day, removes most of the avoidable delay.
Related questions
Do I always get 28 days to complete an auction purchase?
No. Traditional auctions commonly require completion within 28 days of exchange, but some contracts specify 14 or 20 working days and modern method auctions typically allow 56 days. The timescale is stated in the legal pack for each lot, so it is worth checking before bidding rather than after.
What happens if I cannot complete in time?
The seller can serve a notice to complete, charge penalty interest for each day of delay and, if completion still does not happen, rescind the contract and keep your 10% deposit. On a £180,000 purchase that is £18,000 at risk, which is why buyers arrange finance before auction day.
Can I get a mortgage on an auction property at all?
Often yes, if the property is habitable and of standard construction. The difficulty is timing rather than eligibility. Many auction lots are unmortgageable in their current condition, for example with no kitchen or bathroom, and those need bridging or cash first, then a remortgage once works are complete.
How fast can bridging finance actually complete?
One to three weeks is typical for a straightforward case, and some lenders complete in days where the valuation and legal work are simple. The speed depends less on the lender than on how quickly the valuation is booked and how responsive the solicitors on both sides are.
Is bridging not much more expensive than a mortgage?
Per month, yes. Monthly interest of roughly 0.75% to 1.1% plus around 2% in arrangement fees is far above mortgage pricing. The comparison most buyers make is against losing the property or the deposit, and the bridge is normally repaid within months through a sale or remortgage.
Talk it through with us
Every case is different. Call us, message us on WhatsApp, or send us the basics and one of our team will come back to you about auction finance, usually the same working day.