A client has not paid: what can you claim, and what do you write?

$ cat features.md

• UK: statutory interest of 8% over the Bank of England reference rate (base rate on 30 June or 31 December before the debt became overdue), plus fixed compensation of £40, £70 or £100 by debt size.
• Germany: Verzugszinsen of 9 percentage points over the Basiszinssatz for business clients or 5 points for consumers, split per half-year when the rate changes, plus the €40 Pauschale for business clients (§ 288 BGB).
• Shows days overdue, interest per period, the total you can claim and the interest per day from now on.
• Writes the letter: a friendly reminder or a formal demand (UK), a Zahlungserinnerung or Mahnung (Germany), in the language of the law that applies. Print, save as PDF or copy as text for an email.
• Current rates with an "as of" date and links to the Bank of England, Bundesbank, GOV.UK and the law texts; mentions the UK Commercial Payments Bill introduced in May 2026.
• Runs in your browser. Your own details can be remembered on your device if you choose; nothing is sent to a server.

$ cat why.md

Chasing an unpaid invoice is the part of freelancing nobody likes, and most people never claim the interest the law gives them because working it out takes longer than the letter. In the UK the rate depends on the base rate on a date most people do not know; in Germany it changes every half-year. This tool does both in a few seconds and writes the letter, so the reminder goes out the same day. It is also the step after the invoice, which is why it links to my invoice tool.

$ self-host-it

Requirements

Static files, no build step and no dependencies. Any web server works; tests run with Node.js 20+ (node --test tests/).

Built with

HTML, JavaScript

License

MIT

The repository goes public on GitHub soon. Until then, ask me for the code and I'll send you access.