Why an Increase in Working Capital Reduces Cash Flow (The Interview Answer Explained)

If you're prepping for investment banking interviews, you will almost certainly get some version of this question: "Why does an increase in working capital reduce cash flow?"

Here's the short answer: when working capital goes up, cash gets tied up in the business. Either you've sold something but haven't collected the money yet, you've bought inventory you haven't sold, or you've paid your suppliers faster. In every case, cash has left your bank account (or never arrived) even though your income statement might look great.

Let's break down the intuition, walk through real numbers, and make sure you can answer this cleanly and confidently.

First, What "Working Capital" Means Here

In finance interviews and models, "working capital" usually means operating working capital, also called net working capital (NWC):

NWC = Current operating assets − Current operating liabilities

The key word is operating. That means we typically exclude cash and debt.

Common operating assets:

• Accounts receivable (AR)
• Inventory
• Prepaid expenses

Common operating liabilities:

• Accounts payable (AP)
• Accrued expenses
• Deferred revenue

Why exclude cash? Because we're trying to measure how cash changes. If cash were inside working capital, the logic would loop back on itself.

The Core Intuition: Cash Is Stuck

Think of working capital as money parked inside the day-to-day operations of the business. When that parked amount grows, it has to come from somewhere, and that somewhere is your cash balance.

Here's a simple way to picture it:

• A rising asset uses cash. More money is sitting in receivables or on warehouse shelves instead of in the bank.
• A rising liability provides cash. You're holding onto money you owe someone else, so it stays in your account longer.

So when assets grow faster than liabilities, net working capital increases, and cash flow falls.

Line by Line: What's Actually Happening

Accounts Receivable Goes Up

You made a $1,000 sale on credit. The income statement records $1,000 of revenue right away, which flows into net income.

But the customer hasn't paid yet. You have a $1,000 IOU, not $1,000 in cash. So on the cash flow statement, you subtract the increase in AR to correct for revenue you haven't collected.

Inventory Goes Up

You spent cash buying or producing goods that are still sitting unsold. Under accrual accounting, those costs don't hit the income statement until the product is sold (as cost of goods sold).

So the cash is gone, but net income doesn't reflect it yet. The cash flow statement subtracts the inventory increase to capture that outflow.

Accounts Payable Goes Up

This one works the other way. You received goods from a supplier and recorded the expense, but you haven't paid the bill yet.

The expense reduced net income, but no cash actually left. So the cash flow statement adds back the increase in AP. Delaying payment to suppliers is a source of cash.

Deferred Revenue Goes Up

A customer paid you upfront for something you'll deliver later (think annual software subscriptions). You have the cash, but you can't count it as revenue yet.

Net income doesn't include it, so the cash flow statement adds back the increase in deferred revenue.

A Worked Example With Real Numbers

Let's say a company reports the following for the year:

• Net income: $100
• Depreciation & amortization: $40

And here's how its working capital accounts moved:

Net working capital at the start: $150 + $100 − $80 = $170 Net working capital at the end: $200 + $130 − $100 = $230 Increase in NWC: $60

Now calculate cash flow from operations:

CFO = Net income + D&A − Increase in NWC CFO = $100 + $40 − $60 = $80

The company earned $100 on paper but only generated $80 of operating cash flow. The missing cash is sitting in uncollected receivables and extra inventory, partially offset by bills it hasn't paid yet.

Why Growing Companies Feel This the Most

Here's an insight that will make you sound sharp in an interview: working capital usually grows alongside revenue.

More sales typically means more receivables, more inventory, and more payables. If those assets grow faster than liabilities, a growing company needs to keep pumping cash into working capital.

Quick example:

• NWC runs at 10% of revenue
• Revenue grows from $1,000 to $1,200
• NWC goes from $100 to $120
• That's a $20 use of cash, just to support the growth

This is exactly why a profitable company can still run out of cash. If customers pay slowly and inventory piles up, the business can be booking strong earnings while its bank account drains. That's a classic interview follow-up, so have it ready.

Where This Shows Up in Valuation

In a DCF, the change in working capital sits right inside the unlevered free cash flow formula:

Unlevered FCF = EBIT × (1 − tax rate) + D&A − CapEx − Increase in NWC

So if you project NWC increasing every year, your free cash flow drops every year by that amount. That lowers the present value of the business.

When you build projections, NWC items are often forecast as a percentage of revenue or cost of goods sold, or using days metrics like days sales outstanding (DSO) and days inventory outstanding (DIO). Small changes in those assumptions can move valuation noticeably, which is why bankers pay attention to them.

The Flip Side: Negative Working Capital Businesses

Some businesses actually get cash from their working capital as they grow. These companies have negative working capital, meaning operating liabilities exceed operating assets.

Typical examples:

• Subscription businesses that collect cash upfront (big deferred revenue balances)
• Retailers with fast-moving inventory that sell goods before they have to pay suppliers

For these companies, growth can increase cash flow because more sales means more customer cash arriving before costs have to be paid. Mentioning this in an interview shows you understand the concept rather than just memorizing a rule.

How to Answer in an Interview

Keep it tight. Something like:

"An increase in working capital means more cash is tied up in operations. For example, if accounts receivable goes up, the company recorded revenue but hasn't collected the cash yet. If inventory goes up, it spent cash on goods it hasn't sold. Net income doesn't reflect those cash movements, so on the cash flow statement we subtract the increase in working capital to get to actual cash generated."

Then, if you want to add depth, mention that increases in liabilities like accounts payable or deferred revenue work in the opposite direction.

Be Ready for the Three-Statement Follow-Up

A common follow-up: "Walk me through what happens if accounts receivable increases by $10."

• Income statement: No change. (The revenue was already recorded when the sale happened.)
• Cash flow statement: The increase in AR reduces cash flow from operations by $10, so cash falls by $10.
• Balance sheet: Cash is down $10, AR is up $10. Total assets don't change, and nothing changes on the liabilities and equity side, so it still balances.

Common Mistakes to Avoid

• Including cash in working capital. For cash flow analysis, stick to operating items.
• Getting the sign backward. Asset up means cash down. Liability up means cash up. Say it to yourself until it's automatic.
• Including short-term debt. Debt is a financing item, not an operating one. It belongs in cash flow from financing.
• Confusing "working capital" with "change in working capital." The cash flow impact comes from the change between two periods, not the balance itself.

The Bottom Line

An increase in working capital reduces cash flow because cash gets locked inside the business: in money customers still owe you, in inventory waiting to sell, or in bills you've paid faster than before.

Nail the intuition, practice the worked example until you can do it in your head, and remember the growth angle. Do that, and this question goes from a potential stumble to an easy chance to show you really understand how a business turns profits into cash.