DSO Formula for Accounts Receivable (Days Sales Outstanding)
Calculate days sales outstanding from receivables and revenue, interpret the trend, and connect slow collections to net terms, follow-up cadence, and working capital.
Bottom line
DSO translates open receivables into "how many days of sales are still unpaid." Rising DSO with flat terms usually means collections or dispute friction, not a mysterious finance bug. Fix invoice clarity first (net 30 example), then follow-up timing (invoice follow-up email), then liquidity context (working capital ratio).
Is it right for you?
- Pick the same period for average AR and revenue (usually trailing 90 days)
- Use credit sales only if you can separate cash sales in the GL
- Compare DSO to the contractual net term (15, 30, 60)
- Segment by customer or channel before blaming "the whole AR team"
- Pair DSO with follow-up discipline and dispute resolution time
The formula
Days sales outstanding (DSO) = (accounts receivable / credit sales) x days in the period.
Example with a 90-day window: average AR $450,000, credit sales $900,000, days = 90. DSO = ($450,000 / $900,000) x 90 = 45 days.
Some teams use ending AR instead of average AR for a quick dashboard number. Document which version you use so month-over-month comparisons stay honest.
How to read the result
Compare DSO to your stated net terms. If most invoices are Net 30 but DSO runs 52, buyers are paying late on average or disputes are parking balances.
A single large customer can dominate the metric. Export an aging bucket report before you renegotiate terms with everyone.
Seasonal businesses should track DSO by quarter, not only month-end snapshots taken during peak shipping.
Levers that actually move DSO
Print due dates on every PDF and match ERP payment terms codes to the contract (net 15 vs net 30).
Run a timed follow-up ladder instead of ad hoc nagging (invoice follow-up email).
Separate "dispute" threads from "timing" threads so AP clerks can pay undisputed lines.
When buyers ask for card checkout, keep surcharge disclosure clean (surcharge laws by state).
FAQ
Is lower DSO always better?
Not if you starve sales with terms buyers refuse. The goal is DSO near your written terms, not zero at any cost.
Can I use total revenue instead of credit sales?
Only if nearly all sales are on terms. Mixed cash and card businesses should split the denominator.
How is DSO different from collection period?
They use the same math when definitions match. Some ERPs label the report "average collection period."
Where does AP fit?
Paying suppliers late does not fix DSO. It swaps vendor relationships for a temporary cash bump. See ACH vs wire transfer for payout timing that matches real due dates.