calculator tool site

HarborsCalculators

Free online calculators that show their working, with full schedules and PDF and Excel exports.

Industry: Finance & everyday tools
Platform: Astro on Vercel
What we did: Web tool, Astro development, Technical SEO, UI/UX design

Live site, scrolling

The project

The challenge

Most calculator sites hand you a number and stop. No formula, no assumptions, and no way to see why the figure disagrees with the one your bank gave you. HarborsCalculators is Usman’s own product, built to fix that.

What we did

Every calculator updates as you type, shows its formula and assumptions, works an example through, opens the full payment schedule and exports it as a PDF, spreadsheet, CSV or image. Formulas come from primary sources and are covered by unit tests, and everything runs in the browser, so nothing a visitor types leaves their device.

Astro
TypeScript
Vercel
Unit tests

What we built

Eleven calculators across finance, health and maths, from mortgages to BMI
Results that update as you type, with the formula and assumptions on every page
Full month by month schedules with interest and principal split out
PDF, Excel, CSV and image exports generated in the browser, with real number cells
Twenty currencies with local number formats, including lakh grouping
A scientific calculator, a methodology page and an editorial policy