An interest calculator on a website - a small need, delivered fast

The need was specific and unassuming: a simple interest calculator on the website, so anyone could work out for themselves how much is owed on an overdue payment. Tax interest (owed to the Polish tax office and social insurance), statutory interest under the Civil Code, commercial interest on B2B transactions - three modes, one screen.

Works everywhere - and installs like an app

It is a web app: you open it in the browser, on a computer or a phone, with no account to set up. You enter an amount and two dates, pick the type of interest and tap “Calculate”. The rates are current and confirmed on the application’s server, so the result always matches the rules in force - even when the rates change.

And, crucially, it is not only a website. On iPhone and Android the calculator can be added to the home screen and launched like any other app - with its own icon on the phone, full-screen. So the client got a single lightweight solution that is a website and a mobile app at once.

A small need, quickly met

The whole thing is deliberately small - which is exactly why it came together so fast. The client raised the need and, moments later, had a working calculator on their site. One clear need and a quick answer - instead of a multi-week project and a three-page list of requirements.

Why I am writing about it

Because it shows something easy to miss: an idea does not have to be a big deployment to be worth building. A small idea, done well, can take a real nuisance off your plate - and do it right away. Is there one screen like that you are missing? Tell me about it - it can often be built faster than you would think.