About the project

About AuctionMath

AuctionMath is a collection of browser-based reference tools operated by Sidequest 29, LLC. It is designed to help people inspect common auction calculations before bidding, when reviewing an invoice, or while comparing sale records. The tools turn the assumptions entered by a visitor into transparent estimates; they do not determine official auction terms or the value of an item.

How the tools work

The buyer's premium check backs an entered total into a possible hammer price and tests it against the stated bid increment. The buyer-cost estimate applies the entered premium, tax, and fee assumptions. The bid-ceiling tool works backward from a budget and rounds down to the chosen increment. The seller-net estimate subtracts entered commission and costs from the hammer price. The basic calculator evaluates arithmetic expressions, while the historical currency and metal tools request reference data from their named providers.

Each calculator page describes its inputs, calculation assumptions, and a worked example. Rounding conventions, taxes, fee schedules, data coverage, and auction reporting practices can vary. Check the relevant page and compare its assumptions with the original listing, invoice, consignment agreement, and source records.

Data and privacy

The auction calculators run in your browser. Basic calculator history and successful historical rate lookups may be kept in browser storage on your device. Historical currency and metal requests send the selected date, amount, and codes to AuctionMath's API and its data providers so a result can be returned. See the Privacy Policy for more details.

Historical currency results use Frankfurter reference data. Historical precious metal results use Metals.Dev reference data, with Frankfurter used for currency conversion when a conversion is not embedded in the metal data.

Contact and corrections

For questions, accessibility feedback, or a report about a calculator result, contact lauren@sidequest29.com. When reporting a calculation issue, include the tool, inputs, expected result, and steps to reproduce it. Do not include private bidder, payment, or account information.