Free UK Auction Max Bid Calculator

Set your resale and costs

Use completed-sale evidence and the rates published by the auction house and selling platform.

Resale target

Expected resale price

Target profit

Selling fees Percentage of resale price

Postage & selling costs Packaging, ads and other direct costs

Auction charges

Buyer's premium Percentage of hammer price

VAT on premium

VAT on hammer Leave at 0 if it does not apply

Online bidding surcharge Percentage of hammer; include any VAT

Fixed lot fees

Collection or delivery

Maximum hammer bid

£224.41

Stop bidding above £224.41 if you want to protect the entered profit target.

These costs leave no room for a hammer bid. Reduce the target profit or costs, or use a higher evidence-based resale price.

Expected resale price£500.00
Less selling fees−£75.00
Less selling costs−£20.00
Less target profit−£100.00
Allowed all-in auction cost£305.00
Estimated auction charges£80.59
Estimated all-in cost£305.00

Estimate only. Fee bases, VAT treatment, item condition and resale prices vary. Check the lot terms and leave a risk buffer before bidding.

Take the calculator to the lot

The free Chrome extension reads published commission rates on BidSpotter and i-bidder, then checks eBay and Amazon resale margins.

Add to Chrome — free

How to calculate a maximum auction bid

A profitable maximum bid starts at the other end of the deal: what you can realistically keep after selling the item.

Maximum hammer bid = (resale proceeds − selling costs − target profit − fixed auction costs) ÷ auction fee multiplier

Estimate resale proceeds

Use comparable completed sales in similar condition, then subtract marketplace fees, postage, packaging and advertising costs.

Protect your profit

Subtract the profit you require before deciding what remains available for the lot and its auction charges.

Reverse the auction fees

The calculator works backwards through the buyer's premium, VAT, online surcharge, fixed fees and delivery to find the hammer ceiling.

Maximum bid questions

How do I calculate my maximum auction bid?

Start with the expected resale price, subtract selling fees, postage and your target profit, then subtract fixed auction costs. Divide the amount left by the auction fee multiplier created by the buyer's premium, VAT and online surcharge. The calculator above does this in real time.

What should I include in an auction max bid calculation?

Include the buyer's premium, VAT on the premium, any VAT on the hammer price, online bidding surcharge, fixed lot fees, collection or delivery, marketplace selling fees, seller postage and other direct selling costs.

Should my maximum bid include the buyer's premium?

Your maximum hammer bid is the bid shown at auction, before the buyer's premium. This calculator reduces that ceiling so the premium, VAT and other entered charges still fit within your target economics.

How should I choose an expected resale price?

Use realistic completed-sale evidence for the same item and condition rather than an optimistic asking price. Allow for faults, returns, slow-moving stock and price changes before bidding.