Auction Buyer's Premium Calculator: Premium and Total Cost
Work out the buyer's premium on a winning auction bid and what you'll actually pay — the surcharge that turns a 'great deal' hammer price into a meaningfully larger total.
Adjust the inputs and select Calculate for a full breakdown.
Compare Common Scenarios
How the numbers shift across typical situations for this calculator:
| Scenario | Buyer's premium | Total you pay |
|---|---|---|
| 20% on $5,000 | $1,000.00 | $6,000.00 |
| 25% on $2,000 | $500.00 | $2,500.00 |
| 27% on $50,000 (fine art) | $13,500.00 | $63,500.00 |
| 12% on $800 (estate auction) | $96.00 | $896.00 |
How This Calculator Works
Enter the hammer price (your winning bid) and the buyer's premium rate. The calculator multiplies the two to give the premium and shows the total you'll pay. Sales tax and shipping are additional — budget for those on top of this figure.
The Formula
Percentage Add-On
Rate is the tax or tip percentage applied to the amount
Worked Example
A $5,000 winning bid at a 20% buyer's premium adds $1,000, for a total of $6,000 before tax and shipping. Bidders who anchor on the hammer price routinely overpay because the premium is invisible until checkout — a 25% premium plus 8% sales tax turns a $5,000 bid into $6,750. Always set your maximum bid net of the premium you'll owe.
Key Insight
The buyer's premium is auction houses' primary revenue source — and the most-overlooked cost by casual bidders. At a 25% premium, every $100 of bidding costs you $125 before tax. The correct bidding discipline: decide the maximum total you'll pay for an item, then work backward to set your hammer-price bid cap (max total ÷ 1.25 for a 25% premium). Bidders who set their cap on the hammer price alone consistently blow their budget by the premium amount. Premiums have crept up over the decades — what was 10% in the 1990s is 25%+ at major houses today.
Frequently Asked Questions
How is the buyer's premium calculated?
Multiply the hammer price by the premium rate. A 20% premium on a $5,000 winning bid is $1,000, for a $6,000 total before tax and shipping.
What's a typical buyer's premium?
Major houses (Sotheby's, Christie's, Bonhams): 20% to 27%, usually sliding-scale (higher rate on lower-value lots). Regional and estate auctions: 10% to 20%. Online platforms (eBay-style live auctions): 10% to 25%. Always check the specific auction's terms before bidding.
Is sales tax on top of the premium?
Usually yes. Sales tax typically applies to the hammer price PLUS the buyer's premium (the full purchase price), adding another 5% to 10%. Shipping, insurance, and any import duty are additional. The hammer price is often only 70% to 75% of what you actually pay.
How should I set my maximum bid?
Decide the maximum total you're willing to pay (including premium and tax), then work backward. For a 25% premium and 8% tax, divide your max total by 1.35 to get your hammer-price bid cap. Bidding to your max-total on the hammer price alone overspends by the premium and tax.
Why has the buyer's premium increased over time?
It's the auction houses' main margin lever, and competition for consignments has pushed seller's commissions down — so houses raised buyer's premiums to compensate. What was around 10% in the 1990s is 25%+ at major houses today, with periodic increases announced quietly.
Related Calculators
Methodology & Review
The buyer's premium is the hammer price multiplied by the premium rate; the total is the hammer price plus the premium. Major auction houses charge 15% to 30% buyer's premium, often on a sliding scale that drops for higher-value lots. Sales tax and shipping are additional and not modeled here.
Written by Ugo Candido · Last updated May 17, 2026.