Revenue minus expenses. If your revenue is smaller than your expenses, you are making a loss. If your revenue is greater than your expenses, you have made a profit. As always: hings can be a little more complex than that. If your expenses are actually investments, then you may be increasing the value of your business more than would be reflected in a simple statement of profit and loss. But don't pretend something is an investment when it is really a loss. Losses happen.
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