Form Creation

Would a kind soul have any advice on how to create a professional-looking form from an existing Excel spreadsheet? Specifically, I want folks in my office to be able to input a date in one box, click on a "calculate" button, and get the result in another box. The underlying formula is simply arithmetic, nothing fancy. Still, I want the form presentation to look clean and professional.

Any help or suggestions would be MUCH appreciated. The file is attached.