Make a website with a net salary calculator tool

I want to create a website which provides a free tool to enable people to calculate their net salary from their gross salary (UK). Like this site, http://www.netsalarycalculator.net/, but in calculator form. Or like the 'quick calculator' on this site: http://www.thesalarycalculator.co.uk/

The site need only be two pages of content: the homepage, where you input your salary, and the results page, where the calculator outputs your net salary, along with how much tax and national insurance you pay.

Any questions, please don't hesitate to get in touch.