About Reseller Math

Reseller Math is a family of free, fast, no-signup tools for the money side of selling online. Each tool lives on its own subdomain and does one thing well: the 1099-K Checker answers whether a tax form is coming and what it might cost, the Poshmark Offer Calculator reverses a negotiation from the amount you want to keep, and the eBay Promoted Listings Breakeven tool finds the ad rate where promotion stops paying off. This site, resellermath.com, is the hub that ties the family together, with a directory of the tools and editorial on the fees and taxes behind them.

Who runs it

Reseller Math is operated by Crossroads Technologies LLC, a small independent studio that builds focused, single-purpose web utilities. There is no larger platform behind the tools, no account system, and no content farm. The calculators, the fee tables, and the guidance on each site are built and maintained by us directly. Reseller Math is independent and not affiliated with, endorsed by, or sponsored by eBay, Poshmark, Mercari, or any other marketplace; those names are used only to describe how each platform works.

Freshness is the point

Fees and tax thresholds move, and most published guidance freezes at whatever number was current when it was written. eBay revised its final value fee in February 2026; Poshmark and Mercari have each reworked their terms; and the federal 1099-K threshold was rewritten by legislation as recently as mid-2025. Every fee table and threshold in this family lives in a dated data module, and that date is shown next to the numbers. When a platform or the IRS announces a change, the figure and its date are updated together, so you can always see how current the answer you are reading is. We would rather show you the date and let you judge than present a number with no provenance.

What a good tool looks like to us

Every tool in the family follows the same standard. It should be genuinely useful, answering a real question with your own numbers rather than a generic article. It should be instant, running entirely in your browser with no queue and no server round trip. And it should be respectful: no accounts, no sign-up walls, and no data collection inside the tools. Anything you type into a calculator never leaves your device. We would rather ship three small tools that each do their job properly than one sprawling calculator that does everything halfway.

An important limit

These tools produce estimates for planning. They are not tax or financial advice, they do not file anything, and they cannot see the full picture of your finances. For decisions that matter, confirm current fees with each platform and tax questions with the IRS or a qualified tax professional. Found a bug or have an idea for a tool we should build next? Reach us through the contact page.