Defensive Interval Ratio: Formula, Daily Expenditures, and Liquidity Limits

What the Defensive Interval Ratio Measures

The CFA Institute financial ratio list defines DIR using cash, short-term marketable investments, receivables, and daily cash expenditures. That formula does not set a universal 30-to-90-day safety benchmark. It converts selected liquid assets into days at a stated spending rate; it does not establish when each asset becomes spendable or when bills fall due.

How to Calculate DIR Without Double Counting

Use a dated balance-sheet numerator and a clearly identified historical or forecast spending period. A simple income-statement proxy is operating costs less non-cash charges included in those costs, divided by days. That proxy is not an exact cash-flow forecast.

• Add available cash, distinct short-term investments, and net receivables. Exclude inventory and prepaid expenses from this definition; document any stress adjustment to the included assets.
• Assemble the selected operating costs. If cost of sales is separate from operating expenses, include it where required by the definition; if the total already includes it, do not add it twice.
• Subtract only non-cash charges actually included in those selected costs, once. For example, do not subtract all statement-wide depreciation from an expense subtotal that excludes some of it.
• Divide period costs by period days: use an annual numerator of costs with annual days or a quarter’s costs with that quarter’s days. Do not divide annual costs by 90. State any 365/360-day convention.
• Treat changes in inventories, payables, and accrued expenses separately when converting the proxy to a cash budget. Include taxes, interest, debt maturities, capex, and other required payments in a broader liquidity assessment if they are outside your DIR denominator.

Hypothetical Calculation and Collection Stress

Assume $3 million of available cash, $2 million of separate short-term investments, and $4 million of net receivables. Assume selected annual operating costs are $40 million, including $3.5 million of identified non-cash charges. On a 365-day basis, the $36.5 million cost proxy is $100,000 per day. These invented figures are arithmetic examples, not company benchmarks.

Why 90 Days Is Not a Promise of 90 Days of Payments

The hypothetical base result can still conceal a near-term shortfall if a large bill arrives before receivables are collected. Nor does a shutdown necessarily preserve historical costs: severance, penalties, inventory commitments, and collection losses can change the cash requirement. Conversely, discretionary spending reductions can extend a projected runway. Use a dated cash schedule to test those assumptions instead of relabeling DIR as a worst-case forecast.

• Separate confirmed cash from expected collections and record the dates for each. Do not assume every receivable converts within 30 days.
• Compare seasonal businesses at similar reporting dates and reconcile changes in expense classification. A change in DIR can reflect timing rather than a lasting change in liquidity.
• Review available credit separately. A committed facility may have conditions and covenants; undrawn credit is not cash already included in this ratio.

DIR, Quick Ratio, and Cash Runway

Quick ratio compares similar selected assets with current liabilities; DIR compares them with a daily expenditure flow. Cash ratio excludes receivables from its numerator. A startup runway calculation often divides cash by forecast net cash burn, which includes expected inflows and a different spending scope. Neither method is automatically stricter: compare what each includes, its forecast assumptions, and its timing. A zero or negative spending denominator does not produce a useful finite DIR; report the reason rather than a safety score.