Every day an invoice sits unpaid is a day your cash is working for your customer instead of for you. Days sales outstanding, or DSO, is the number that puts a figure on that delay. The good news is that DSO is one of the most improvable metrics in finance: small, consistent changes to how you invoice and follow up can take days off it within a quarter. This guide explains what DSO is, what a healthy number looks like, and the concrete levers that bring it down.
What is days sales outstanding?
DSO is the average number of days it takes to collect payment after a credit sale. A DSO of 45 means that, on average, money arrives about 45 days after you invoice. It is a cash-flow measure, not a profit measure: a business can be profitable on paper and still run short of cash because its DSO is too high and the money is stuck in accounts receivable.
How do you calculate DSO?
The standard formula is straightforward:
- DSO = (accounts receivable ÷ total credit sales) × number of days
Pick a period, use the credit sales for that period, and the number of days in it. Here is a worked example. Suppose at the end of a 90-day quarter your accounts receivable is £600,000 and your total credit sales for the quarter were £3,000,000. Then DSO = (600,000 ÷ 3,000,000) × 90 = 0.2 × 90 = 54 days. On average it takes you 54 days to turn a sale into cash in the bank.
What counts as a good DSO?
There is no universal target — a good DSO is one that sits close to your payment terms. If you invoice on net 30 and your DSO is 38, you are collecting reasonably well, because a few days of slippage is normal. If you invoice on net 30 and your DSO is 65, more than a month of sales is sitting uncollected beyond terms, and that gap is the problem to attack. Compare DSO to your own terms and to your own trend over time, not to a number from a different industry.
Why does high DSO hurt?
High DSO ties up cash you have already earned. That cash cannot pay suppliers, fund payroll, or cover growth, so you may borrow to bridge the gap and pay interest on money customers already owe you. A rising DSO is also an early warning: it can signal billing errors, unhappy customers disputing invoices, or weakening credit quality in your customer base. Watching the trend matters as much as watching the number.
What are the levers to reduce DSO?
DSO comes down when you remove friction and delay from the whole order-to-cash cycle. The most effective levers are:
- Invoice fast and accurately. Send the invoice the moment work is delivered, and make sure the amount, PO number and details are correct. A wrong invoice resets the clock.
- Set clear payment terms. State the due date, accepted methods and terms plainly on every invoice, and agree them before the sale rather than after.
- Offer easy payment methods. The simpler it is to pay — card, bank transfer, direct debit, a one-click link — the sooner you are paid.
- Check creditworthiness and set credit limits. Vet new customers and cap exposure so a single slow payer cannot dominate your receivables.
- Send proactive reminders. A friendly note before the due date, then a structured follow-up sequence after it (a dunning process), keeps your invoice near the top of the pile.
- Prioritise by value and age. Chase the largest and oldest balances first; that is where the cash and the risk are concentrated.
- Resolve disputes quickly. A query held open is an invoice unpaid. Route disputes to an owner and close them fast.
- Offer early-payment incentives carefully. A small discount for early settlement can help, but price it so the cost does not outweigh the cash-flow gain.
- Review an AR aging report regularly. The aging report groups receivables by how overdue they are and shows exactly where to focus each week.
Common pitfalls
- Starting too late. If the first reminder goes out only after the due date, you have already lost time. Contact before the invoice is due.
- Treating every account the same. A blanket chase wastes effort on small balances and under-serves the big ones.
- Ignoring disputes. An unanswered query quietly becomes an aged debt.
- Over-discounting. Permanent early-payment discounts can erode margin more than the faster cash is worth.
- Watching only the headline number. A stable average DSO can hide a growing tail of very old, high-risk invoices — always read the aging report underneath it.
Start with the two cheapest levers: invoice the day work is done, and send a reminder before each due date. Measure DSO every month, read the aging report behind it, and let the trend — not a single month — tell you whether it is working.
Frequently asked questions
What is a good DSO number?
There is no single target. A good DSO is one that stays close to your payment terms, so net 30 terms with a DSO in the high 30s is healthy, while a DSO far above your terms signals a collection problem to fix.
How is DSO calculated?
Divide accounts receivable by total credit sales for a period, then multiply by the number of days in that period. For example, 600,000 in receivables against 3,000,000 of credit sales over 90 days gives a DSO of 54 days.
Why is a high DSO bad for cash flow?
A high DSO means cash you have already earned is tied up in unpaid invoices. That money cannot fund payroll, suppliers or growth, so you may have to borrow to bridge the gap while customers still owe you.
What is the fastest way to reduce DSO?
Invoice immediately and accurately, and send reminders before the due date rather than after. Those two habits remove the most common sources of delay without straining customer relationships.
FulcrumGrid Collection
Bring your DSO down in one place
FulcrumGrid Collection helps you track receivables, aging and reminders together, so you can see what is overdue and follow up before cash slips away.