Days Sales Outstanding Formula (DSO) and Excel Example
Summary
DSO = (Accounts receivable ÷ Credit sales) × Number of days. It estimates how many days, on average, it takes customers to pay. A distributor with $1.402M of receivables at quarter-end and $3.735M of credit sales over the 92-day quarter has a DSO of about 34.5 days.
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Days sales outstanding (DSO) formula
DSO = (Ending accounts receivable ÷ Credit sales in the period) × Days in the period- Ending accounts receivable: Unpaid customer invoices at the end of the period, from the balance sheet or AR aging report.
- Credit sales: Sales made on invoice terms during the period. Exclude cash or card sales paid at the time of purchase.
- Days in the period: Calendar days covered by the credit sales figure: 30 or 31 for a month, 90–92 for a quarter, 365 for a year.
How to calculate days sales outstanding (DSO) in Excel and Google Sheets
Excel, using the cells in the worked example below:
=D4/SUM(C2:C4)*SUM(B2:B4)Worked example
A B2B packaging distributor sells on net-30 terms and wants its Q3 DSO for the monthly cash meeting. Everything it sells is invoiced, so all sales are credit sales.
| Month | Days | Credit sales | Ending AR |
|---|---|---|---|
| July | 31 | $1,240,000 | $1,288,000 |
| August | 31 | $1,310,000 | $1,365,000 |
| September | 30 | $1,185,000 | $1,402,000 |
- Credit sales for the quarter = 1,240,000 + 1,310,000 + 1,185,000 = $3,735,000.
- Days in the quarter = 31 + 31 + 30 = 92.
- Ending AR at September 30 = $1,402,000.
- DSO = 1,402,000 ÷ 3,735,000 × 92 = 34.5 days.
- September alone: 1,402,000 ÷ 1,185,000 × 30 = 35.5 days. Receivables rose while sales fell, which is the early signal to chase overdue accounts.
Result: 34.5 days DSO for Q3
How to interpret days sales outstanding (DSO)
Compare DSO with your payment terms: on net-30 terms, a DSO in the low-to-mid 30s means most customers pay roughly on time, while a DSO drifting well past 40 means a growing share is paying late. Because DSO divides a point-in-time balance by a flow, it moves with sales volume: a big sales month at period-end raises DSO even if nobody paid late. Pair it with an AR aging report (current, 1–30, 31–60, 61–90, 90+ days past due) to see whether the change is collections or just timing.
Common mistakes
- Including cash sales in the denominator. That makes DSO look shorter than customers actually take to pay.
- Using total-year sales against a single month-end balance in a seasonal business. Match the sales period to the balance date, or use a countback method month by month.
- Comparing DSO across periods of different length without adjusting the day count (28 vs 31 days changes the result by roughly 10%).
- Reading DSO alone. Write-offs reduce AR and make DSO look better; check bad-debt expense and the aging buckets too.
Calculate days sales outstanding (DSO) with Better Analyst
Connect your data or upload a spreadsheet, then ask in plain English. Better Analyst writes and runs the calculation and shows the steps, so you can check the number.
- “Calculate monthly DSO for the last 12 months from our invoices and payments tables.”
- “Build an AR aging report with 0–30, 31–60, 61–90 and 90+ day buckets by customer.”
- “Which customers have pushed our DSO up the most this quarter?”
Usually calculated from: 
Microsoft SQL Server, PostgreSQL, MySQL, Snowflake, Google Sheets, Google BigQuery.
Further reading
Frequently asked questions
What is a good DSO?
Should I use average or ending accounts receivable for DSO?
How is DSO different from the AR turnover ratio?
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