I've been reading Capital off and on for months and this is a seemingly pretty important difference that I don't understand. Is there a difference between surplus labor and profit, and if so, what is it? Any explanations, links, or chapters in Capital I should check out are appreciated.
in managerial economics, "profit" is typically broken down into various slices, especially for the sole proprietor who might pay themselves out of "what's left", may even be the only employee, may have different debt types (operating loans vs infrastructure loans). so they talk about "returns" i.e.
Return to Labor/Management, and Capital: is the money left after you've paid your material and operating costs, but haven't paid down the principal on any debt (after making minimum payments on their debt servicing) or yourself as manager/worker. this is how a lot of self employed, sole proprietor, single owner/operators keep books and conceptualize profits. it works, but it's limited and can lead to issues if the income is variable and doesn't really do much for making decisions.
better practice is to bake your salary (as manager/employee) into the budget and maybe even come up with a plan to pay down debts faster. paying yourself a fixed salary allows one to conceptualize what their hourly rate is and start analyzing the decisions they make about clients they take on, how to spend their time, and definitely what improvements to make to your infrastructure, etc. obviously numbers don't capture drudgery or enjoyment, but they do matter in knowing what would squeeze you (and be worth cutting your own salary for a while) and what might sink you.
there's another distinction of "accounting profitability" vs "economic profitability". accounting profitability is money leftover after you do your thing in a given period of time. economic profitability is that same amount minus what you would have netted doing something else (ie opportunity cost lost by running your business a certain way, or not working for someone else).
there aren't always analogues of these concepts to marxian economics because managerial economics are micro and Marx is towards the macro end, but I strongly believe understanding managerial economics (which can be learned fairly easily in like 1 class in college) can make one a better marxian analyst of how an organization can be more equitably organized, not to mention it helps a lot if you want to do your own thing and avoid exploiting yourself unnecessarily.