Hi,
I have already built different kind of online calculators and I work a lot of finance software development, so this is absolutely my field of expertise.
I have several questions for you:
Is this a part of the website you are building (like a page, or module), or this is the core of the website (the only thing it is built of)?
How do we solve the design - do you have already design for the site, or I should build it? Do you have anything against using comercial templates for base of the design?
When you say person should enter data only one time, do you mean one time per session, or like one time at all (any time person is back on site, data will be available)? Do we store user data (register/login), or it's open for public use?
These are the questions for now, I'm sure I will have more of them once we start with development. Since I am very interested in this project, please contact me for discussion of further details.
Kind regards,
Nikola