Days Sales Outstanding (DSO) and Accounts Receivable Aging: How Fast Do Customers Pay?

Calculating and Interpreting DSO

Choose a consistent period (a month, quarter, or year) and use credit sales only if cash sales are significant. For an annual calculation, DSO = receivables ÷ annual credit sales × 365. A DSO well above your payment terms suggests late payers: if your terms are net 30 and DSO is 45, customers are paying about two weeks late on average. DSO also rises when a few large invoices are very overdue. Industry norms vary: retail and consumer businesses have low DSO, while business-to-business and government contracts commonly have 45 to 60 days or more. Track DSO monthly and compare with your own history.

The best possible DSO (BPDSO) uses only current receivables and shows how low DSO could be if no invoices were overdue; the gap between DSO and BPDSO indicates collection problems.

Reading an Aging Report

An accounts receivable aging report groups unpaid invoices by how overdue they are: current, 1 to 30 days, 31 to 60, 61 to 90, and over 90 days. Suppose receivables of $450,000 are: current $270,000 (60%), 1 to 30 days $90,000 (20%), 31 to 60 days $54,000 (12%), 61 to 90 days $22,500 (5%), and over 90 days $13,500 (3%). The older an invoice, the less likely it will be collected: a common rule of thumb is that collectability drops sharply after 90 days. Review the report weekly, identify the customers behind the old balances, and decide on follow-up. Reserve for bad debts based on the age profile, such as 1% for current, 5% for 31 to 60 days, and 25% or more for over 90 days.

How to Improve Collections

Invoice promptly and accurately, with clear terms and due dates. Send reminders before the due date, on the due date, and at regular intervals afterward. Offer convenient payment methods, such as online payments and automatic debits. Consider early-payment discounts where the economics work (2/10 net 30 is equivalent to a 37% annualized rate), deposits for large jobs, and late fees as allowed by law and contract. Check customer credit before extending terms, and set credit limits. Escalate overdue accounts by phone, then to a formal demand, and eventually collections. Keep customer relationships in mind: a call to ask what is causing the delay can resolve disputes quickly.

Limits of DSO

DSO can be distorted by seasonality or fast growth: if sales spike at the end of the period, DSO looks higher than collections performance justifies. The countback method, which counts back through monthly sales until receivables are covered, reduces this distortion. Combine DSO with the aging report and the collection effectiveness index (CEI) for a full picture.