I’m develop a software tool to aid my work, but now I’m wondering if it’s better to sell the software when it’s done?

I'm totally new to software development, so there is a lot I don't understand. I'm making a tool to help me in my line of work; it's basically a custom calculator that cannot be found for free or online. Only massive companies sell it, and it's usually part of an expensive package.

I'd like to develop it for my own person productivity, but now I'm nervous that if I spend all this time creating it, it could be snatched up and sold by someone else. However, I'm not sure where to even begin if I do plan on selling it.

tl;dr – if you had a valuable small software tool, would you charge for it? Or is it too much hassle and not worth it?