The rate at which something makes money is its profitability. The profitability of your dog walking business means you'll be able to buy that new video game you've been wanting.
The goal of almost every business is to increase profitability — in other words, to grow the amount of money it takes in. Profitability usually has to do with cash, although it originally meant a more general kind of benefit or usefulness. The Latin root is profectus, "success or progress," which is fitting when you think about how the a business's success is usually judged based on its profitability.