Auction Fee & Buyer’s Premium Calculator
The hammer price is only the headline. Add the buyer’s premium, flat fees, and tax to see what a lot truly costs — and the markup hiding behind the winning bid.
What you actually pay
Know the real price before you bid
Every auction quotes the hammer price, but no buyer actually pays only that. The buyer’s premium is a fixed percentage the house takes from you on top of the winning bid, sales tax usually applies to the combined figure, and some sales add a flat per-lot fee. Two houses advertising the same estimate can leave you paying very different totals once those layers are stacked.
Running the numbers first does two things: it stops the final invoice from surprising you, and it feeds straight into your maximum bid. If a house charges a 25% premium, every dollar you bid really commits about $1.25 plus tax — so the fee schedule should pull your bidding ceiling down, not the other way around.
Frequently Asked Questions
What is a buyer's premium?
A buyer's premium is a percentage that the auction house adds to the hammer price and charges to the winning bidder. So if you win a lot at $200 with a 20% premium, you owe $240 before tax. Premiums are how most auction houses make their money from buyers, and they vary widely — from around 10% at some traditional houses to 20–25% or more, and often a few percent at online-only marketplaces.
Is sales tax charged on the premium too?
In most places, yes — sales tax is calculated on the hammer price plus the buyer's premium, not on the hammer price alone. This calculator taxes the combined total by default, which matches how the majority of auctions bill it, but you can turn that off if your jurisdiction differs.
What does effective markup mean?
It's the total you pay expressed as a percentage above the hammer price. A 20% premium with 8% tax on top doesn't add up to 28% — the tax also applies to the premium, so the real markup is a little higher. Seeing that single number makes it easy to compare the true cost of buying at different houses.
Estimates only. Premium rates, flat fees, and tax rules vary by auction house and location — always check the terms of sale.