How UK Auctions Work: The True Cost of Winning

Most resellers lose money on their first auction lot — not because they overpaid at the hammer, but because they didn't understand the fees stacked on top. Understanding these costs before you bid is the single most important skill a reseller can develop.

The hammer price is just the start

When you win a lot at a UK auction, the price you pay in the room (or online) is called the hammer price. It's the last number shouted by the auctioneer. What most beginners don't realise is that the hammer price is usually just 60–70% of what you'll actually pay.

Here's the full cost stack:

| Cost | Typical rate | What it is | |------|-------------|------------| | Hammer price | — | What you bid and won | | Buyer's premium | 18–25% | Auction house fee on top of hammer | | VAT on buyer's premium | 20% | VAT applied to the premium only | | VAT on hammer (sometimes) | 20% | On some commercial goods sales | | Postage / collection | £5–£80+ | Getting the item to you | | Packaging | £1–£5 | Materials to relist safely |

A worked example

You win a lot for £100 hammer price. The auction house charges 24% buyer's premium.

• Hammer price: £100
• Buyer's premium (24%): £24
• VAT on premium (20%): £4.80
• Total paid: £128.80

Now add £8 postage and £2 packaging. Your item cost you £138.80 before you've listed it anywhere.

If you sell it on eBay for £160 and eBay takes 12.8%:

• eBay fee: £20.48
• Net received: £139.52
• Profit: £0.72

That's why knowing your maximum bid before you bid is the difference between profit and loss.

Buyer's premium varies by auction house

UK auction houses typically charge between 18% and 30% buyer's premium. Some charge different rates for online bidders vs in-room. Always check the specific auction's terms before registering.

Common UK auction house premiums:

• i-bidder platform houses: Usually 20–24% + VAT
• The Saleroom: 20–25% + VAT
• Large commercial auctioneers: 18–20% + VAT
• Small local auctioneers: Sometimes as low as 15%, but can be 28%+

VAT: who pays it and when

VAT at UK auctions appears in two places:

1. VAT on the buyer's premium — almost always applies at 20%
2. VAT on the hammer price — only applies when the seller is VAT-registered selling as a business

If you're buying from a local house selling household clearance, hammer price VAT usually doesn't apply. If you're buying from a commercial liquidator or B2B seller, it often does. The lot listing will say "VAT on hammer" or "VAT applicable" if this is the case.

Online bidding surcharges

Bidding through third-party platforms (i-bidder, BidSpotter, Lot-tissimo, Barnebys) often adds an extra 3–5% surcharge on top of everything else. Always read the full bidding terms before a sale.

The max bid formula

The Arbitrage AI Max Bid Calculator uses this formula so you never overpay:

max_hammer = (estimated_resale - platform_fee - postage - packaging - target_profit)
             ÷ (1 + buyers_premium% × (1 + vat%))

Set it up once in your profile. Every lot card shows your personalised ceiling in large orange text — you don't even need to do the maths.

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Key takeaway: The hammer price is never the final price. Add buyer's premium, VAT on premium, postage, and packaging before you decide on a maximum bid. Use the Max Bid Calculator on every lot to protect your margin automatically.

→ Run your first auction scan to see lot scores and max bids in real time