Working capital, and why it eats cash

Here's the thing nobody tells you in your first accounting class: a company can be growing fast, booking record profits, and still run out of cash. Not because it's losing money. Because its cash is stuck inside the business.

That stuck cash is working capital. Understand it and you understand why profit and cash are two different animals, which is the single idea that separates people who "get" the three statements from people who memorized a script.

What working capital actually is

Net working capital (NWC) is the money tied up in the short-term stuff you need to operate. The clean definition bankers use:

$\text{NWC} = \text{Current operating assets} - \text{Current operating liabilities}$

Note the word operating. We deliberately strip out cash and any short-term debt. Cash is what we're trying to explain, not part of the tangle we're measuring. Debt is a financing decision, not an operating one. So the real line items are:

| Operating assets (uses of cash) | Operating liabilities (sources of cash) | | --- | --- | | Accounts receivable (AR): sales you booked but haven't collected | Accounts payable (AP): bills you owe suppliers but haven't paid | | Inventory: product sitting on shelves | Accrued expenses: wages, rent, etc. owed but not yet paid | | Prepaid expenses: things you paid for early | Deferred revenue: cash collected before you deliver |

The mental model: assets are cash you've handed out and are waiting to get back. Liabilities are cash other people have handed you and you're sitting on. That framing tells you which way the cash moves, and it's the part beginners flip.

The rule that trips everyone up

An increase in an operating asset uses cash. An increase in an operating liability is a source of cash. Read that twice.

Why? Say you sell $100 of product on credit. You recognize $100 of revenue on the income statement, so net income goes up. But no cash came in. Your AR went up $100 instead. That $100 of "profit" is sitting in a customer's promise to pay, not in your bank account. On the cash flow statement, the increase in AR is a subtraction from cash. It has to be, because you added the profit but never got paid.

Flip it. When AP rises because you bought inventory on credit and haven't paid the supplier yet, you're holding onto cash you technically owe. That's a source of cash.

Change in NWC is what hits cash, not the level

This is the subtlety. The cash flow statement doesn't care about the balance of working capital. It cares about the change from last period to this one.

$\Delta\text{Cash from WC} = -\,\Delta(\text{operating assets}) + \Delta(\text{operating liabilities})$

The minus sign in front of the asset change is the whole game. Assets up, cash down.

Quick example. A company grows sales 20% this year. AR climbs from $100 to $130 and inventory from $50 to $70. AP rises from $40 to $55.

| Line item | Change | Cash impact | | --- | --- | --- | | Accounts receivable | +$30 | -$30 | | Inventory | +$20 | -$20 | | Accounts payable | +$15 | +$15 | | Change in NWC | +$35 | -$35 |

NWC grew by $35, so the business consumed $35 of cash just to support growth, before spending a dime on CapEx or paying a cent of interest. The faster it grows, the more cash it swallows. That's the paradox: growth is expensive, and working capital is where the bill shows up.

The cash conversion cycle, in plain terms

If you want one number that captures how efficient a business is with working capital, it's the cash conversion cycle. It answers a simple question: from the day you pay for inventory to the day you collect from the customer, how many days is your cash locked up?

Three pieces, all measured in days:

• DIO (Days Inventory Outstanding): how long product sits before you sell it.
• DSO (Days Sales Outstanding): how long customers take to pay you after the sale.
• DPO (Days Payable Outstanding): how long you take to pay your suppliers.

$\text{Cash Conversion Cycle} = \text{DIO} + \text{DSO} - \text{DPO}$

You want DIO and DSO low (sell fast, collect fast) and DPO high (pay suppliers slowly, using their money in the meantime). A shorter cycle means less cash trapped in operations.

Say inventory sits 60 days, customers pay in 45, and you pay suppliers in 30. Your cycle is $60 + 45 - 30 = 75$ days. For 75 days, your own cash is funding the operation. Shave DSO to 30 and the cycle drops to 60 days, freeing up cash you can put to work elsewhere. Same profit, better business.

When negative is a gift

Here's the contrarian part. Some of the best business models run on negative working capital, and it's a feature, not a problem.

Think about a subscription software company, or a gym, or a magazine. Customers pay upfront before the service is delivered. That cash lands as deferred revenue, a liability. The company gets to use your money for months before it "earns" it. Deferred revenue doesn't touch the income statement until the service is delivered, so it's pure cash float sitting on the balance sheet.

Grocery and discount retail is similar. They sell inventory for cash in days but pay suppliers on 30 or 60 day terms. Their suppliers are effectively financing their shelves. Negative working capital means growth generates cash instead of consuming it. When you see it, you're usually looking at a business with real pricing power or structural leverage over its customers and suppliers.

For how this feeds valuation, see the DCF, explained, and to make sure you can trace any line item through all three statements, start with walk me through the three statements.