You don’t have to be CPA or MBA to start or run a business. You don’t have to understand debits and credits, or be able to balance your books. But there are some financial facts you just plain need to know. Here’s a list.

1. Every single dollar in Accounts Receivable (AR) is a dollar less in cash. AR is the standard for business-to-business transactions. You deliver the goods or service along with an invoice, and the client/customer pays you later. That money shows up as sales in the Profit & Loss (P&L), but it’s not in the bank; it’s in AR. This brings up AR aging, collection days, and a flock of related concepts that are all important because a business can die over failing to collect on AR – even profitable businesses choke on AR. Corollary: if you sell to consumers, in cash, check, or credit cards, this is not as important. And if you manage to get business customers to pay you a deposit in advance, that helps a lot too.
2. Every dollar in inventory is a dollar less in cash. As with money you have in AR, money spent on inventory doesn’t show up in the P&L until you sell the stuff and it becomes cost of goods sold. So whatever is in inventory isn’t in your bank account. As with AR, companies that are profitable in the P&L can run out of cash in the bank because they got their inventory constipated. In some extreme cases, expenses get misdirected to inventory, and the system clogs up with inventory that pretends to be assets and creates a fiction that ends up with the reality of no cash in the bank. Corollary: most service businesses don’t have inventory to worry about, and those that do need inventory usually have less of a problem because they need less inventory per transaction.
3. Every dollar in Accounts Payable (AP) is a dollar more in cash. Most businesses buy stuff on credit, meaning they get the stuff along with an invoice they have to pay in a few weeks. Almost nobody pays bills in cash immediately. Ideally, you finance inventory and AR with the money you owe to your vendors. You have to manage the pull between paying on time, paying late, and stretching AP without getting a reputation for late payments or a bad credit rating. It takes management. That satisfaction you get from paying everything immediately, and not owing anything to anybody – that’s not good financial management.
4. Debt repayment doesn’t show up in P&L. It costs you money, but you won’t see it if you don’t track cash flow. The interest portion of payments is an expense, so that shows, but principal – debt repayment – doesn’t show up. You have to watch and plan for it.
5. Buying assets doesn’t show up in P&L. It takes money to buy your assets (equipment, plant, land, furniture, etc.) but those don’t count as expenses, so you don’t see them in P&L.
6. Fixed vs. variable costs matter. That’s because the trade-offs come up often and matter a lot, and this area is full of choices you can make. Do you hire the person as an employee or contract out for skills? Fixed costs are generally lower than variable costs, but they also increase the risk.
7. Sunk costs don’t matter. It’s so not intuitive. We so often think we have to continue down some path because we’ve already spent so much money on it. It’s hard to let that go. But the money already spent is a sunk cost. You don’t get it back by spending more. So decide based on whatever decision criteria make sense, in a specific situation; money already spent is never a good reason, by itself, to spend more.

For the record, this post started as one of my answers on Quora: The original question was What are the most important financial concepts an entrepreneur should know?