Auction Fees Calculator UK: The True Cost of a Lot Before You Bid
If you bid £100 at a UK online auction, you will not pay £100. Once the buyer's premium, platform surcharge and VAT are stacked on top, the invoice usually lands somewhere between 30% and 48% above your winning bid. This is a plain-English auction fees calculator for UK buyers: what every line on the bill means, what BidSpotter and i-bidder actually charge, and how to work backwards to a maximum bid that still leaves you a profit.
The 30-second answer
Expect to pay roughly 30–48% over the hammer price at a typical UK online auction once buyer's premium, platform fees and VAT are added. Here is the maths on a £100 lot where VAT applies across the board:
| Line on the invoice | Amount |
|---|---|
| Winning bid (hammer price) | £100.00 |
| Buyer's premium (20%) | £20.00 |
| Internet surcharge (3%) | £3.00 |
| VAT (20% on the lot) | £24.60 |
| Total to pay | £147.60 (47.6% over your bid) |
That £47.60 of extras on a £100 bid is not a worst case — it is an ordinary one. The Auction Bid Calculator shows this all-in figure on the lot page as you bid, so you never have to run it on a phone calculator mid-sale — try it on a live lot.
The four layers of an auction bill
Every auction invoice is built from up to four layers. Only the first is the number you watch on screen while the lot climbs.
Hammer price: the bid, not the cost
The hammer price is simply your winning bid — the figure the gavel falls on. It is the starting point for everything else, and on most bidding screens it is the only number shown in real time. Treat it as a subtotal, never the total.
Buyer's premium: the auctioneer's cut
The buyer's premium is a percentage the auction house adds to your winning bid. Across UK salerooms it typically runs 15–30%; the houses listed on BidSpotter range from about 7% to 25% depending on the room. It goes to the auctioneer rather than the seller, it is non-negotiable, and it is charged on top of the hammer. If you have ever wondered how much auction houses charge buyers, this is the main answer — a buyer's premium calculator is really just hammer price times the premium rate.
VAT: the bit everyone misses
VAT is where auction maths gets slippery. Two things are always true: VAT applies to the buyer's premium and to every platform fee on essentially every lot. What changes is the VAT treatment of the hammer price itself, and that depends on how the lot is sold:
- Margin-scheme lots — most second-hand goods sold by general salerooms. Under GOV.UK's auctioneers' margin scheme guidance, VAT is accounted for by the auctioneer within their margin, so there is no separate VAT line on the hammer and nothing for you to reclaim.
- "+VAT" lots — trade, commercial and ex-business stock. Here VAT (usually 20%) is added to the hammer price, and you get a proper VAT invoice, so a VAT-registered buyer can reclaim it.
This is what "20% buyer's premium plus VAT" means in a listing: the 20% premium is charged, and VAT is then added to that premium (and to the hammer as well on trade lots). It is not a flat 40% — it is a 20% premium with 20% VAT applied to the relevant parts.
Platform and extra fees
Online marketplaces add their own layer on top of the house premium:
- BidSpotter charges an internet surcharge of around 3% for bidding live through its platform, per BidSpotter's own support pages.
- i-bidder adds a platform premium of 3.5% plus VAT, per i-bidder's fee guidance.
- Lotting, loading and handling charges can apply per lot at some rooms.
- Storage often runs £1–£5 per day once you pass the collection deadline.
- Late payment can lift the premium — some houses move it from 20% to 25% if you miss the payment window.
A worked example: £100 and £500 lots
Put the layers together and the pattern is clear. Both columns below assume a lot with a 20% buyer's premium and VAT applying across the board — a "+VAT" trade lot on BidSpotter with a 3% internet surcharge. Houses vary, so treat this as the shape of the bill rather than a fixed quote.
| Line on the invoice | £100 lot | £500 lot |
|---|---|---|
| Hammer price (your bid) | £100.00 | £500.00 |
| Buyer's premium (20%) | £20.00 | £100.00 |
| Internet surcharge (3%) | £3.00 | £15.00 |
| Subtotal | £123.00 | £615.00 |
| VAT (20%) | £24.60 | £123.00 |
| Total to pay | £147.60 | £738.00 |
| Over your bid | +47.6% | +47.6% |
See this number before you bid
Auction Bid Calculator adds the all-in cost to the lot page itself and updates it as the bid rises, so you never do the sums by hand or get caught out by the invoice. Try it on a live BidSpotter lot.
What UK auction platforms charge (July 2026)
Rates correct as of July 2026. The buyer's premium is set by each auction house, so the ranges below are typical rather than universal; the platform fee is charged on top of whatever the saleroom sets.
| Platform | Buyer's premium | Platform / internet fee | VAT treatment | Watch out for |
|---|---|---|---|---|
| BidSpotter UK | ~7%–25% (set by house) | ~3% internet surcharge | VAT on premium and fees always; on the hammer only for "+VAT" lots | Storage charges after the collection deadline |
| BidSpotter US | Set by house | Internet surcharge applies | US sales tax may apply; UK VAT rules do not | Currency conversion and import costs |
| i-bidder | 15%–30% typical (set by house) | 3.5% + VAT platform premium | VAT on premium and fees; hammer depends on the lot | Late-payment premium uplift |
| Independent saleroom | 15%–30% typical | Often none in the room; a platform fee if bidding online | Mostly margin scheme; "+VAT" on trade lots | Lotting and loading fees; some rooms are cash on collection |
Buying to resell? The second fee stack
If you are buying from auction to resell on eBay, your all-in auction cost is only the first fee stack. The second one lands when you sell.
On eBay's 2026 UK rate card, business sellers pay a final value fee of roughly 6.9%–14.9% by category, plus £0.40 per order — and, the part that catches people out, the fee is calculated on the total including postage, not just the item price. Add promoted listings and the effective take can climb to around 22% of the sale. Private sellers now sell for free on eBay UK, but if you are flipping stock regularly you are a business seller in eBay's eyes.
Here is what that does to a flip that looks healthy on paper. You buy a lot for £100 hammer, which costs you £147.60 all-in, and you sell it on eBay for £220 including £12 postage:
| Line | Amount |
|---|---|
| Sold price (incl. £12 postage) | £220.00 |
| eBay final value fee (14.9%) | −£32.78 |
| Fixed order fee | −£0.40 |
| Postage paid to the courier | −£12.00 |
| Your all-in auction cost | −£147.60 |
| Net profit | £27.22 |
Selling at £220 against a £147.60 cost looks like a comfortable 50% mark-up. After both fee stacks are paid, the real number is about £27 — near enough 12% of the sale. That gap is exactly why the auction bid calculator models eBay fees alongside auction costs; our eBay fee tools break the second stack down line by line.
How to work out your true maximum bid
Because every fee is a percentage, you can run the whole thing backwards. Start from what the item actually sells for and strip each layer away:
- Start with your target sold price on eBay.
- Subtract eBay fees and postage.
- Subtract the profit you want to keep.
- Divide what is left by your all-in auction multiplier — about 1.476 for a lot with a 20% premium, a 3% surcharge and 20% VAT across the board.
- The result is your maximum hammer bid. Bid a penny more and the margin is gone.
Worked through: a target sold price of £220, minus roughly £45 in eBay fees and postage, minus a £30 profit target, leaves £145 of headroom. Divide by 1.476 and your maximum bid is about £98. If the room pushes past that, let the lot go. The extension does this reverse calculation for you — set a target margin and it shows the maximum bid straight on the lot page.
FAQ
What is a buyer's premium?
A buyer's premium is a percentage the auction house adds to your winning bid, typically 15–30% in the UK. It is paid by the buyer, goes to the auctioneer rather than the seller, and is non-negotiable. You pay it on top of the hammer price on almost every lot.
Do I pay VAT on the buyer's premium?
Yes. VAT is charged on the buyer's premium and on platform fees on essentially every lot, including margin-scheme lots. What varies is whether VAT is added to the hammer price itself, which depends on how the lot is sold.
Why is my auction invoice 25–30% more than my winning bid?
Because the bid is only the hammer price. Buyer's premium, a platform or internet surcharge and VAT stack on top, and together they commonly add 30–48% to what you bid. The invoice total, not the hammer, is your real cost.
Can I reclaim the VAT if I'm buying for my business?
Only on "+VAT" lots that come with a standard VAT invoice, usually trade, commercial or ex-business stock. Margin-scheme lots account for VAT inside the auctioneer's margin, so there is no separate VAT figure for a VAT-registered buyer to reclaim.
How much are the fees on BidSpotter and i-bidder?
On top of each auction house's own premium, BidSpotter adds an internet surcharge of around 3%, and i-bidder adds a platform premium of 3.5% plus VAT. Both are charged in addition to the buyer's premium set by the saleroom.
How do I work out my maximum bid when flipping to eBay?
Take your target eBay sold price, subtract eBay fees, postage and the profit you want to keep, then divide what is left by your all-in auction multiplier (about 1.476 for a 20% premium, 3% surcharge and 20% VAT). The answer is the most you can bid at the hammer and still hit your margin.
Auction maths is not hard, but it is easy to forget under time pressure while a lot is climbing. We built Auction Bid Calculator because we were tired of running these sums on a phone calculator mid-sale — it puts the all-in cost and the resale margin on the lot page, so the only decision left is whether the number works.
See the real cost before you bid
Auction Bid Calculator shows commission, VAT and eBay fees live on the lot page — so you know your true cost and margin before you commit. Free to use on BidSpotter and i-bidder, no account needed.