Case study
CalcBloc: tax calculators, salary API and open tax data
CalcBloc, our own product: free paycheck and tax calculators for the US and 12 more countries, a public salary and tax API, CC BY 4.0 tax tables for 37 countries on GitHub, Zenodo and Kaggle, and open-source client libraries and plugins.
At a glance
- Type
- Our own product, built and operated by itmarkerz
- Calculators
- Paycheck and tax calculators for the US and 12 more countries, with Spanish and German versions
- API
- Free JSON API with an OpenAPI file: 50 calls a day without a key, 5,000 with a free key
- Open data
- Tax tables for 37 countries (242 tables, 9,427 rows, 841 official sources), CC BY 4.0, on GitHub, Zenodo and Kaggle
- Libraries
- Python, TypeScript/Node, PHP and R, open source on GitHub
- Integrations
- WordPress plugin, Google Sheets add-on, Excel add-in, browser extension and MCP server, open source on GitHub
- Stack
- Next.js and TypeScript, Redis, headless WordPress for articles, on our own server behind Cloudflare
Why we built it
Salary and tax calculators rarely show where their rates come from, so a result is hard to check. We wanted calculators where every rate is taken from the official tax agency that sets it, with the source linked and the date it was last checked, and where the same data is open for anyone to reuse.
What we built
A calculator site for the US and 12 more countries: take-home pay, income tax and employer cost, including state, province and other regional rules, plus a tax-table page for each country. Every figure links to its official source.
A public JSON API on the same calculation engines, covering take-home pay, employer cost, a two-country comparison and tax tables, with an OpenAPI file. It works without a key for 50 calls a day per IP address, and a free key gives 5,000 a day.
The tax tables as open data: income tax brackets and social security rates for 37 countries as CSV and JSON, with a data dictionary and a Frictionless Data Package descriptor, under CC BY 4.0. The dataset is on GitHub, archived on Zenodo with a DOI, and on Kaggle.
Client libraries and integrations built on the same tables: Python, TypeScript/Node, PHP and R packages, a WordPress plugin, a Google Sheets add-on, an Excel add-in, a browser extension that shows take-home pay next to salaries on job listings, and an MCP server so AI assistants can use the data. All are open source on GitHub.
What it shows
Product ownership end to end: collecting data from official sources, calculation engines, a public API, open data publishing and developer tooling, all run in production by us.
Related services and industries
Have a similar project?
Tell us what you need to build or change. We reply within one business day (IST).