Allow me to suggest a different take on this. I think what you are saying is that you have a relatively new product that is selling and sales are growing perhaps slowly. It is not loosing money if you don't consider the value of your time, but probably not making as much as you would hope or perhaps you think you could make doing something else.
The math part is easy, you can plug your numbers into a spreadsheet and see how much you will make in the future if things continue the way they are.
The two things you should consider are:
1) What else would you do with the resources (your time perhaps) that you would free up by shutting down the business?
2) Is there something that could happen to dramatically improve the business?
Only you know about number 1, but number 2 is interesting because many businesses fail simply because they shut down too soon, generally because they ran out of money (under capitalized). It takes time to build a reputation and become known. Also some businesses are seasonal, retail in the US generally makes most of its money just before Christmas. Starting a store in June and shutting down in October would miss all the Christmas shoppers for example. You need to give the business enough time to gather enough data.
Assuming you have enough experience and data, and it looks like something needs to change for the business to really take off, then consider what that might be and how realistic it is that it will happen.
Some things are beyond your control, such as when the US was attacked on 9/11. Suddenly sales of American flags sky rocked over night and manufacturers could sell all they could make. There is really no way to predict something like this, but it could happen for your product.
The other thing to consider is what could you change to make a big difference. An example is Orville Redenbacher with his popcorn. He was selling the popcorn part time and not making much money. He was frustrated and hired a marketing firm to help him. The suggested he call it "gourmet popping corn" and the rest is history. Sometimes a simple change like that can make all the difference.
What generally does not work is doing nothing with a belief like "our product is so much better that soon everybody will want it". Better doesn't always win, the question is what will be the defining event that will change things? Consider free, open source software. Many will tell you why Linux and Open Office are so much better than Microsoft Windows and Office. Maybe so, but why should I believe that this year will be the year that suddenly people stop buying Windows computers? What is the defining event that will change everything?