Working Capital

What working capital really is

Operating working capital is the cash trapped in receivables and inventory, less the financing you get from payables.

Working capital is the cash a company has tied up in running its day-to-day operations. When you sell on credit, you book revenue today but collect the cash later — that gap sits on the balance sheet as accounts receivable. When you buy or build product before you sell it, cash leaves now and comes back only when the goods sell — that is inventory. And when your suppliers let you pay later, they are effectively lending you money interest-free — that is accounts payable. Operating working capital nets these together.

Operating Working Capital = Accounts Receivable + Inventory − Accounts PayableWe deliberately exclude cash and short-term debt; those are financing items, not the operating cash cycle. This is the working capital a model forecasts.

The crucial idea for modelling is that working capital is not a number on the income statement — it is a balance-sheet position whose change moves cash. A company can report rising net income and still be starved for cash if receivables and inventory are ballooning faster than profit. That divergence between accrual profit and cash is exactly what the cash flow statement exists to reconcile, and working capital is the biggest moving part in that reconciliation for most operating businesses.

Profit is an opinion, cash is a fact The income statement records a sale when it is earned; the bank account only moves when cash actually changes hands. Working capital is the bridge between the two — and the place where fast-growing companies most often run out of money.

• Accounts receivable: cash you are owed by customers — a use of cash while it grows.
• Inventory: cash locked up in unsold goods — a use of cash while it grows.
• Accounts payable: cash you owe suppliers — a source of cash (free financing) while it grows.

Forecasting with the days method

Convert each account into days of revenue or COGS, then project the days and reverse the formula.

Working-capital accounts scale with the business, so you never forecast their dollar value directly. Instead you express each account as a number of days — how many days of sales are sitting in receivables, how many days of cost are sitting in inventory, how many days of cost you owe suppliers — and then forecast the days. Days are stable, comparable, and easy to reason about, which is why every desk uses them.

DSO = (Accounts Receivable / Revenue) × 365How many days, on average, it takes to collect cash from a sale. Tied to the revenue driver.

DIO = (Inventory / COGS) × 365How many days of cost of goods sold are held as inventory. Tied to the COGS driver.

DPO = (Accounts Payable / COGS) × 365How many days you take to pay suppliers. Also tied to COGS, since payables fund purchases of goods.

Notice which driver each ratio uses: receivables scale with revenue because they arise from sales, while inventory and payables scale with COGS because they arise from the cost of buying and making product. Getting the driver right is half the discipline. Once you have forecast the days, you reverse the formula to get the dollar balance: receivables become Revenue × DSO / 365, inventory becomes COGS × DIO / 365, and payables become COGS × DPO / 365.

1. Calculate each account's historical days (DSO, DIO, DPO) from the most recent actuals.
2. Decide on a forecast assumption for each — hold flat, trend toward a peer benchmark, or model an efficiency improvement.
3. Apply the days to the forecast revenue (for AR) or forecast COGS (for inventory and AP) to get each balance.
4. Take the period-over-period change in each balance — that change is what hits cash.

Anchor to history before you forecast Always compute the trailing days first. If a company has run at 45 DSO for five years, a forecast of 30 DSO is a strong claim about collections that you need a reason for. Start from where the business actually operates.

The cash conversion cycle

DSO + DIO − DPO measures how many days cash is trapped between paying suppliers and collecting from customers.

The three days metrics combine into a single, powerful summary: the cash conversion cycle (CCC). It measures the number of days between when a company pays cash out for inventory and when it finally collects cash back from customers. The shorter the cycle, the less cash the business needs to fund its own operations — and the more growth it can finance from within.

CCC = DSO + DIO − DPODays waiting to collect, plus days holding inventory, minus days of supplier financing. Lower is better; some businesses run it negative.

A negative cycle is a competitive weapon When DPO exceeds DSO + DIO, suppliers and customers fund the business's growth for free. Retailers like this can expand without raising capital — every new store is partly financed by the people they buy from.

When you model an improvement in the cycle — say a procurement team that stretches payables or a logistics upgrade that cuts inventory days — you are forecasting a one-time release of cash in the year it happens. That cash shows up in operating cash flow, not on the income statement, which is precisely why working capital deserves its own analysis rather than being buried in the P&L.

Why the change in working capital moves cash

An increase in working capital is a use of cash; a decrease is a source — and it lives in operating cash flow.

Here is the single most important — and most counter-intuitive — rule in this unit. An increase in operating working capital is a use of cash, and a decrease is a source of cash. It feels backwards because more receivables and more inventory are assets, and assets feel like a good thing. But growing those assets means cash has gone out the door and not yet come back: you have shipped product you haven't been paid for, or built inventory you haven't sold.

Cash Flow Effect = − ( Working Capital_this period − Working Capital_last period )The minus sign is the whole point. WC up → cash down. WC down → cash up.

• Receivables rise → you booked the sale but haven't collected → cash is used.
• Inventory rises → you paid to build stock that hasn't sold → cash is used.
• Payables rise → you're holding onto suppliers' money longer → cash is a source.
• The net of these three changes is the 'changes in working capital' line in operating cash flow.

Growth is not free A profitable, fast-growing company can run out of cash precisely because growth inflates receivables and inventory faster than profit generates cash. The income statement looks great while the bank balance shrinks — this is how solvent-on-paper businesses fail.

Wired into the Cash Flow tab for you In The Cash Flow Projector, the engine derives DSO, DIO, and DPO from the company's SEC history, projects each balance from your assumptions, takes the period-over-period change, and posts it to the Cash Flow tab — with the correct sign — automatically. Change a single days assumption and operating cash flow, the cash balance, and the balance-sheet plug all re-settle while the three statements stay in balance.