About numlane
numlane is a small collection of free calculators built and maintained by Joschka Bieri, an independent app developer based in the Emmental, Switzerland.
Why these tools exist
Most calculators online either hide their formula, use rates that went stale months ago, or stop at a single number. numlane takes the opposite approach: each tool is built around one real decision (what to charge, what you are owed, what a listing really earns), uses the current official numbers, and gives you something you can keep, such as a spreadsheet with live formulas or a printable letter.
How each calculator is made
- Primary sources first. Rates and fees are taken from the issuing body: the Deutsche Bundesbank for the Basiszinssatz, eBay's own fee pages, the model providers' pricing pages. Each page lists its sources and the date they were checked.
- Formula in plain sight. Every tool shows how the result is calculated and includes a worked example you can reproduce by hand.
- Tested. The calculation engines are covered by automated tests built from worked examples before a page goes live.
- Kept current. Rates that change on a schedule (half-yearly interest rates, platform fee updates, model prices) are re-checked on that schedule. If something looks out of date, please write to the address in the imprint.
What numlane is not
The calculators give information, not legal, tax or financial advice. For decisions with legal consequences, check the linked official source or ask a professional.
Privacy in one paragraph
Calculations run in your browser; what you type is not sent to a server. Google Analytics loads only if you allow it in the cookie banner. Details are in the privacy policy.