How to Forecast Working Capital: DSO, DIO, DPO

To forecast working capital, project each operating line on its own driver instead of guessing the total. Receivables follow revenue through days sales outstanding (DSO). Inventory follows cost of goods sold through days inventory outstanding (DIO). Payables follow cost of goods sold through days payable outstanding (DPO). Wall Street Prep frames the job the same way: forecasting working capital means mechanically linking operating relationships across the statements. The year-on-year change then flows into free cash flow.

TL;DR

• Forecast AR on revenue via DSO, inventory on COGS via DIO, payables on COGS via DPO.
• Hold the ratios flat to history unless you can defend a change.
• The cash conversion cycle equals DIO plus DSO minus DPO.
• Never include cash, marketable securities, or debt in the operating schedule.
• The schedule output is the change in NWC, which the DCF subtracts.

Practice inside this guide

Practice Forecast Working Capital: DSO, DIO, DPO

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A fast-growing company reports strong and rising EBITDA every quarter, but its operating cash flow is consistently much lower and occasionally negative. What could explain the gap, and why does this matter to an analyst?

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What are the three forecasting formulas?

Each ratio converts a balance into days, then the forecast runs the formula in reverse:

$\text{DSO} = \frac{\text{Receivables}}{\text{Revenue}} \times 365$

$\text{DIO} = \frac{\text{Inventory}}{\text{COGS}} \times 365$

$\text{DPO} = \frac{\text{Payables}}{\text{COGS}} \times 365$

Receivables scale with sales because credit terms attach to revenue. Inventory and payables scale with cost of goods sold because they attach to what the company buys and makes. Wall Street Prep states the turnover versions of the same idea: DSO from receivables turnover, inventory days from inventory turnover, and payables days from payables turnover over COGS.

Together the three ratios give the cash conversion cycle, which Wall Street Prep defines as DIO plus DSO minus DPO: the days between paying for inputs and collecting from customers.

What does a worked schedule look like?

Take a teaching example with revenue of 1,000 dollars, COGS of 600 dollars, and historical ratios of DSO 36.5, DIO 30.4, and DPO 24.3 days. The forecast is mechanical:

• Receivables: 36.5 / 365 x 1,000 = 100 dollars.
• Inventory: 30.4 / 365 x 600 = 50 dollars.
• Payables: 24.3 / 365 x 600 = 40 dollars.
• Operating NWC: 100 + 50 - 40 = 110 dollars.

If next year revenue grows 10 percent to 1,100 dollars and COGS grows to 660 dollars with flat ratios, NWC becomes 121 dollars and the change of 11 dollars is subtracted from free cash flow. Growth consumed cash even though margins never moved. That is the working capital versus cash flow wedge in miniature. For where the change lands in the full model, see how to forecast cash flows in a DCF and unlevered versus levered free cash flow.

What breaks most working-capital forecasts?

Four mistakes, all avoidable. First, forecasting NWC as a flat percent of revenue ignores that payables follow COGS, not sales, so margin shifts silently corrupt the schedule. Second, leaving cash or debt in the operating lines double counts them against the valuation bridge; the schedule covers operating accounts only, per our operating working capital scope. Third, improving ratios every year without a business reason bakes phantom cash into the DCF. Fourth, forgetting that other operating current assets and liabilities exist: accrue them as a percent of the relevant expense base rather than dropping them. State each assumption aloud in an interview. "Flat to the three-year average" is a defensible answer when the business is stable.

Frequently Asked Questions

Should working capital be forecast as a percent of revenue?

Only as a rough check, never as the schedule. Receivables track revenue but inventory and payables track COGS. A single revenue percentage breaks whenever margins move.

What DSO, DIO, and DPO should I assume?

Start with the company's own three-year history. Change a ratio only for a stated reason such as new payment terms, a different sales mix, or a disclosed working-capital program.

What is the cash conversion cycle?

DIO plus DSO minus DPO. It measures the days between cash going out for inputs and cash coming back from customers. A shorter cycle means operations fund themselves faster.

Do I include deferred revenue in the forecast?

Yes when it is operating, which covers most subscription businesses. Cash collected before revenue is recognized is an operating liability, and its change is a source of cash.

How does the change in NWC enter the DCF?

Subtract the increase from NOPAT plus D and A minus capex. An NWC increase means cash got tied up in operations, so free cash flow falls by that amount. See walk me through a DCF for the full bridge.

Sources

• Wall Street Prep, "Working Capital": https://www.wallstreetprep.com/knowledge/working-capital/ (checked September 2026)
• Corporate Finance Institute, "Working Capital Formula": https://corporatefinanceinstitute.com/resources/financial-modeling/working-capital-formula/ (checked September 2026)
• Wall Street Prep, "Cash Conversion Cycle": https://www.wallstreetprep.com/knowledge/cash-conversion-cycle-ccc/ (referenced from the Working Capital guide, September 2026)