Days’ sales outstanding (DSO) measures the number of days it takes to convert receivables into cash and is calculated by dividing the number of days in the period by the accounts receivable turnover ratio. An increasing DSO (decreasing receivables turnover) may be an indication of lower quality revenue; that is, the longer it takes to collect from customers, the more likely the receivables will turn into bad debt.

Days’ inventory on hand (DOH) is equal to the number of days in the period divided by inventory turnover ratio and it measures the number of days it takes to sell inventory. An increasing DOH may be indicative of obsolete inventory.

Analysts should compare changes in the core operating margin over time and look for negative nonrecurring (e.g., restructuring charges, asset impairments, and write-downs) or non-operating items that occurred when the ratio increased. This may be the result of misclassifying an operating expense.