How to Calculate Working Capital in an Interview (DSO, DIO, DPO Walkthrough)

"Walk me through how you'd calculate working capital, and tell me whether an increase is good or bad for cash flow" is a staple question in accounting and FP&A interviews — and it's one candidates trip over surprisingly often, mostly because they memorize the formula without practicing the actual calculation on numbers. Here's how to approach it methodically, using DSO, DIO, and DPO.

Step 1: Pull the Right Balance Sheet Line Items

You need five inputs, typically for two consecutive periods so you can measure the change: Revenue, COGS, Accounts Receivable, Inventory, and Accounts Payable. Revenue and COGS come from the Income Statement; the other three come from the Balance Sheet.

Step 2: Convert Each Balance Sheet Item Into a "Days" Metric

This is the step most candidates skip in practice, and it's exactly where interviewers probe. Each metric uses a specific balance sheet item over the income statement driver that actually generates it:

• DSO = (Accounts Receivable / Revenue) × 365 — receivables are driven by revenue, since that's what generates the invoice
• DIO = (Inventory / COGS) × 365 — inventory is carried at cost, so it's measured against COGS, not revenue
• DPO = (Accounts Payable / COGS) × 365 — payables fund the purchase of goods, which shows up in COGS

A common interview trap: using Revenue as the denominator for all three. It's only correct for DSO — DIO and DPO should both use COGS.

Step 3: Combine Into the Cash Conversion Cycle

CCC = DSO + DIO − DPO. This single number tells you how many days of cash are tied up in the operating cycle between paying for inputs and collecting from customers. If CCC is lengthening period over period, more cash is getting stuck in the business.

Step 4: State the Source-or-Use Conclusion Explicitly

This is the part interviewers listen for most closely. Compute NWC = Accounts Receivable + Inventory − Accounts Payable for each period, then take the difference. An increase in NWC is a use of cash (more capital tied up in operations); a decrease is a source of cash (capital freed up). Say this explicitly — "NWC increased by $15m, which is a use of cash" — rather than just stating the dollar figure and leaving the interviewer to infer the direction.

Practice With Real Numbers

The best way to get comfortable with this sequence is to run it end-to-end on an actual two-year data set. The Working Capital Deep Dive case walks through exactly this: computing DSO, DIO, DPO, and CCC across two years, then determining whether the resulting change in NWC was a source or use of cash — the same structure you'll be expected to reproduce live in an interview.

The Conceptual "Why" Behind This Framework

This four-step walkthrough is the "how do I calculate it" companion to a deeper conceptual question: why does net working capital matter in the first place, and how does the Cash Conversion Cycle connect to the free cash flow build. What Is Net Working Capital? Cash Conversion Cycle Explained unpacks that underlying logic in more depth — useful background if the interviewer pushes past the mechanical calculation into "why does an increase in NWC use cash in the first place?"

A Numerical Variation to Practice

To make sure the sequence is understood rather than memorized from a single walkthrough, work through a different company: Revenue of $500m, COGS of $350m, Accounts Receivable of $60m, Inventory of $45m, and Accounts Payable of $55m. DSO = ($60m / $500m) × 365 = 43.8 days. DIO = ($45m / $350m) × 365 = 46.9 days. DPO = ($55m / $350m) × 365 = 57.4 days. CCC = 43.8 + 46.9 − 57.4 = 33.3 days. Running the same four steps against a different mix of revenue, COGS, and balance sheet figures, rather than only reciting one company's numbers, is what separates a candidate who understands the mechanic from one who has memorized a single worked example.

Notice that this second company's CCC of 33.3 days is meaningfully shorter than a typical industrial manufacturer's, since its DPO of 57.4 days almost fully offsets its combined DSO and DIO of 90.7 days. That's a useful sanity check to run mentally during an interview: if your computed CCC looks unusually short or unusually long relative to what you'd expect for that industry, it's worth double-checking whether you used Revenue or COGS as the denominator for each metric before presenting the answer.

DSO, DIO, and DPO Formula Reference

How This Connects to the Free Cash Flow Build

Once you've calculated the change in NWC and labeled it correctly as a source or use of cash, the next step in most interviews is plugging that figure into an unlevered free cash flow forecast, alongside D&A and CapEx adjustments. How to Calculate Free Cash Flow From Net Income (Interview Walkthrough) covers exactly where the NWC adjustment fits into that larger build, so the working-capital calculation you just practiced doesn't stay an isolated exercise.

Why DSO Is Worth Recognizing Beyond This Calculation

Days Sales Outstanding isn't unique to this working-capital walkthrough — it's the same metric used to flag revenue quality concerns like channel stuffing and bill-and-hold arrangements, covered in What Is Revenue Quality? Channel Stuffing, Bill-and-Hold, and Other Red Flags Explained. A rising DSO in a routine working-capital calculation can mean nothing more than slower collections, but the same rising DSO paired with unusual quarter-end revenue patterns can be a red flag worth investigating further. Recognizing that DSO shows up in both contexts demonstrates a more complete grasp of the metric than treating it as a one-off formula memorized for a single question type.

Common Ways Candidates Lose Points on This Question

A few recurring mistakes show up when candidates answer this prompt under interview pressure. Some use Revenue as the denominator for DIO and DPO instead of COGS, which inflates or deflates the days figures and signals a shaky grasp of the mechanics. Others compute DSO, DIO, and DPO correctly but never state the source-or-use conclusion out loud, leaving the interviewer to do that translation themselves. Still others get the sign convention backwards in the CCC formula, adding DPO instead of subtracting it. Avoiding these three slips is what separates a clean answer from a shaky one.

How This Question Escalates at the Associate Level

At the analyst level, interviewers are typically satisfied once a candidate can pull the right line items, compute DSO, DIO, and DPO correctly, and state whether a change in NWC is a source or use of cash. At the associate level, the question often extends into forecasting judgment — for instance, asking a candidate to project DSO, DIO, and DPO forward based on management guidance or industry benchmarks, or asking how a deteriorating DPO trend might signal a supplier relationship under strain. Being ready to move from "here is the mechanical calculation" to "here is what this trend implies going forward" is what separates a strong associate-level answer from a merely correct analyst-level one.

A Pre-Interview Checklist for This Question

Before an interview where this exact topic might come up, it's worth confirming: can you name the five inputs needed (Revenue, COGS, AR, Inventory, AP); can you state the DSO, DIO, and DPO formulas with the correct denominators without hesitating; can you build the CCC formula with the correct sign convention; and can you state a source-or-use conclusion explicitly rather than just reporting a dollar figure. If any of these feel shaky, revisit the full worked case and the companion conceptual article linked above before attempting this question again.

Industry Patterns Worth Knowing Before the Interview

The typical magnitude of DSO, DIO, and DPO varies widely by industry, and knowing the pattern sharpens an answer well beyond a generic formula. Retailers tend to run low DIO and DSO (fast inventory turnover, mostly cash or card sales) but can negotiate long DPO with suppliers, often producing a short or negative CCC. Industrial manufacturers typically carry higher DIO, since raw materials must be converted into finished goods before sale, pushing CCC higher. Software and subscription businesses often show minimal DSO, DIO, and DPO altogether, since there's little physical inventory and revenue is frequently collected upfront. Being able to name which industries run high or low on each metric demonstrates a more grounded understanding than treating every company's ratios as similar.

Why This Question Is a Favorite Screening Tool

Interviewers return to this exact four-step structure because it tests whether a candidate can move fluently between the income statement and the balance sheet, translate a set of ratios into a single days-based metric, and state the cash flow implication out loud without prompting. Because this calculation sits at the intersection of accounting, FP&A, and cash flow modeling — three areas that show up constantly in finance interviews — mastering this four-step sequence, rather than memorizing one company's numbers, is a high-leverage way to prepare for this entire question family.

The Takeaway

The four-step order in this article — pull the right line items, convert each to a days metric, combine into the CCC, and state the source-or-use conclusion explicitly — is a template, not a script tied to any one company's numbers. Practicing it against a handful of different revenue, COGS, and balance sheet figures, rather than memorizing the original walkthrough verbatim, is what makes a candidate resilient to however the interviewer happens to phrase the question, and it's the foundation for connecting working capital changes to the free cash flow build whenever that comes up next.