What it means
The current ratio and quick ratio compare liquid assets with current liabilities, which answers the question "can the company pay what it owes?". The defensive interval ratio asks a different question: "how long can the company keep operating?".
It compares liquid assets not with liabilities but with the daily cost of running the business, and expresses the answer in days. The reframing matters because liabilities are not the only cash demand on a business; wages, rent, suppliers and utilities have to be paid every day whether or not there are sales, and a company with a comfortable current ratio can still run out of money if its revenue stops and its costs do not.
Defensive assets are those that can be turned into cash quickly without disrupting operations: cash, bank deposits, marketable securities, and trade receivables, which will be collected in the normal course. Inventory is excluded, because selling it requires the business to keep operating, and because it may not be saleable quickly at book value.
Daily operating expenses are the cash costs of running the business for a year, divided by 365: cost of sales, selling and administrative costs, and interest, less non-cash charges such as depreciation and amortisation, which consume no cash. Some versions of the ratio include only cash and securities in the numerator, giving a stricter measure of how long the company could survive if customers stopped paying as well as buying.
The ratio is most informative for businesses whose income is uncertain or lumpy. A start-up with no revenue yet uses the same arithmetic under the name of runway: cash divided by monthly burn gives the months until the money runs out, which is the defensive interval expressed in months.
A consultancy or contractor that depends on a few large clients can see how long it could survive the loss of one. A seasonal business can see whether it holds enough liquidity to cover the quiet months.
A company in a crisis, such as a product recall or a regulatory suspension, can see how long it has to fix the problem. For a mature business with steady sales, the ratio is less pressing but still a useful check that the balance of liquidity is not being run too thin.
Interpreting the number requires judgement about what could actually happen. Fifty days is ample for a supermarket, whose customers pay daily and whose revenue will not stop; it is thin for a defence contractor awaiting a single payment on a single contract.
The relevant comparison is with the length of the disruption the business might plausibly face: the time to replace a lost customer, to restart production after an incident, to arrange emergency finance. Where the interval is shorter than that, the business should hold more liquidity or arrange committed facilities, which do not count as defensive assets but serve the same purpose.
The ratio has limitations. Receivables are counted at book value, but some will be collected late or not at all, and in a crisis that affects the business's customers too, collections slow exactly when they are needed.
Operating expenses are taken as fixed, but a business under stress can cut discretionary spending, which lengthens the real interval. And the ratio says nothing about liabilities: a company might have a long defensive interval and still face a loan repayment it cannot meet.
It is a complement to the current ratio and to a cash flow forecast, not a substitute.
In practice
Real-world examples.
Example
A restaurant chain with cash of $1,500,000 and daily cash costs of $60,000 has a defensive interval of 25 days, which its board judges too short given the risk of a temporary closure, and it arranges a committed overdraft.
Example
A biotechnology company reports a defensive interval of 30 months, which is the figure investors care about, since it shows how long the company can fund research before it needs to raise money again.
Example
An engineering consultancy calculates its interval at 70 days including receivables and 20 days excluding them, and concludes that its liquidity depends on clients paying on time.
Think of it
“Defensive interval shows how long you could keep the lights on if all revenue suddenly stopped.
Formula
Calculation
Defensive interval ratio (days) = Defensive assets / Daily cash operating expenses
Defensive assets = Cash + Marketable securities + Trade receivables
Daily cash operating expenses = (Annual operating expenses minus Non-cash charges) / 365
Runway (months) = Cash / Monthly cash burn
Worked example. A distribution company holds cash of $2,400,000, short-term investments of $600,000 and trade receivables of $3,000,000. Its annual operating expenses, including cost of sales and administration, are $27,000,000, of which $1,200,000 is depreciation.
- Defensive assets = $2,400,000 + $600,000 + $3,000,000 = $6,000,000
- Cash operating expenses = $27,000,000 minus $1,200,000 = $25,800,000; daily = $25,800,000 / 365 = about $70,700
- Defensive interval = $6,000,000 / $70,700 = about 85 days
- Strict version (cash and securities only): $3,000,000 / $70,700 = about 42 days
The company's current ratio is 1.8, which looks comfortable. The defensive interval adds the information that if revenue stopped, the company could meet its running costs for less than three months, and for six weeks if its customers stopped paying too.
Worked example: start-up runway. A software start-up has $4,000,000 of cash and no revenue. Its cash operating costs are $250,000 a month.
- Daily cash expenses = $3,000,000 / 365 = about $8,200
- Defensive interval = $4,000,000 / $8,200 = about 487 days, or 16 months of runway
- After a planned hiring round takes costs to $400,000 a month ($4,800,000 a year, about $13,150 a day), the interval falls to about 304 days, or 10 months, which tells the board that the next funding round must close within that timeCase study
Seen in the real world.
A consultancy with annual cash operating costs of $29,200,000 ($80,000 a day) held $800,000 of cash and $2,400,000 of receivables: defensive assets of $3,200,000 and a defensive interval of 40 days. The managing partner regarded the position as normal for the firm and had never arranged a bank facility, on the principle that the firm had never needed one.
Then its largest client disputed a $1,500,000 invoice for a project it considered incomplete and stopped paying while the dispute was argued. The client was also the source of 25% of the firm's new work, which paused too.
The defensive interval, recalculated excluding the disputed receivable, was $1,700,000 / $80,000 = 21 days, and with revenue reduced by a quarter, the firm was consuming cash at about $20,000 a day net. The finance manager's forecast showed the firm unable to pay its monthly salary bill of $1,800,000 within seven weeks.
The response had to be fast and on several fronts. The firm arranged a $2,000,000 revolving credit facility with its bank, which took three weeks and required personal guarantees from the partners, a condition the bank would not have imposed on a firm that had approached it in normal times. It chased every other receivable and reduced its days sales outstanding from 45 to 32 within a month, releasing about $1,000,000.
Partners deferred their own drawings. The dispute was settled at $1,200,000 after two months.
The firm survived, but the managing partner's review concluded that a 40-day interval had been too thin for a business dependent on a handful of clients and paid monthly in arrears, and that the facility should have been arranged when it was not needed. The firm set a policy of holding defensive assets of at least 90 days of cash costs, of which at least 45 days in cash or committed facilities, and reported the interval to the partners monthly.
Watch out
Common mistakes.
- Including inventory in defensive assets; it cannot be turned into cash without continuing to operate, which is the assumption the ratio removes.
- Using total operating expenses including depreciation and amortisation, which overstates the daily cash outflow and understates the interval.
- Relying on the interval without questioning the receivables; in a crisis that affects the company's customers, collections slow when they are needed most.
Questions
People also ask.
What is the difference between the defensive interval ratio and the quick ratio?
The quick ratio compares liquid assets with current liabilities and gives a multiple; the defensive interval compares liquid assets with daily operating costs and gives a number of days. The quick ratio asks whether the company can pay what it owes; the defensive interval asks how long it can keep running.
What is a good defensive interval?
It depends on how quickly the business could replace lost revenue or arrange finance. Thirty to ninety days is typical for established trading companies; start-ups and research companies measure it in months of runway and aim for twelve to twenty-four; businesses with concentrated customers or interruption risk should hold more.
Do committed bank facilities count?
Not in the ratio as usually calculated, which uses assets on the balance sheet. But an undrawn committed facility serves the same purpose, and many companies report the interval both with and without it.
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