Buying at auction to resell: how to check the numbers

A lot can look like a bargain against its resale value and still lose money once fees, VAT and your selling costs are counted. Work the numbers out before you bid.

The sum that matters

Profit = resale price − selling fees − all-in cost of buying (including repairs and delivery)

A worked example

You win a lot at £800 hammer, with a 20% premium, a 4% online fee and VAT on the fees. You expect to resell it for £1,500, and the platform you'll sell on takes 10%.

Expected resale price	£1,500.00
Selling fees (10%)	-£150.00
All-in cost of buying (£800 hammer)	-£1,030.40
Estimated profit	£319.60

Margin vs markup

Profit can be expressed two ways, and mixing them up leads to bad decisions:

Margin is profit as a share of the resale price: £319.60 ÷ £1,500 = 21.3%
Markup is profit as a share of what you paid: £319.60 ÷ £1,030.40 = 31.0%

Both are correct, but they're very different numbers. BidCalc uses margin on the resale price.

Work backwards to a maximum bid

If you want a 20% margin, the most you can spend in total is £1,500 × (1 − 0.10 − 0.20) = £1,050. Divide by the fee factor of 1.288 and your highest bid is £815.22. At that price, your profit is £300, which is 20% of £1,500.

What people forget

Repairs and cleaning, which belong in the cost.
Delivery in and out, and storage while you wait to sell.
An optimistic resale price. Use a cautious figure, not the best price you've ever seen.
Your time, which isn't free.
VAT status. It affects what you can reclaim and charge, so see the VAT guide and ask your accountant.

How BidCalc helps

Tick "I plan to resell this" under the total, then enter your expected resale price, selling fees and target margin. BidCalc shows your profit and margin, and the highest bid that still reaches your target. Your PDF summary includes the resale estimate. For vehicles, the Copart calculator adds a repair cost too.

Open the £800 example Copart calculator

General information only, not tax or financial advice. Auction houses set their own fees and terms, so always check the conditions of sale and confirm the details with the auction house before you bid.