Days Sales Outstanding (DSO): Formula and Examples
Learn the days sales outstanding (DSO) formula, how to calculate it with worked examples, what a good DSO looks like and practical ways to bring it down.
Quick answer: Days sales outstanding (DSO) is the average number of days it takes to collect payment after a credit sale. The DSO formula is: accounts receivable ÷ credit sales for the period × number of days in the period. If you have $108,000 in receivables and made $270,000 of credit sales in a 90-day quarter, DSO = 108,000 ÷ 270,000 × 90 = 36 days.
Days sales outstanding is the single number that tells you whether your invoicing and collections are working. If it creeps up, cash is getting stuck with your customers even when sales look healthy. This guide explains the DSO formula, shows several worked examples, covers what "good" looks like and lists practical ways to lower it, starting with clear invoices from our free invoice generator.
What is days sales outstanding?
When you sell on credit, you deliver first and get paid later. The money owed sits in accounts receivable until the customer pays. DSO converts that balance into days: roughly how many days of sales are currently waiting to be collected.
Because it is expressed in days, DSO is easy to compare with your payment terms. A business on Net 30 terms with a DSO of 32 is collecting roughly on time. The same business with a DSO of 58 is, on average, waiting almost a month longer than agreed.
DSO is also called average collection period. Some definitions compute the two slightly differently, but they measure the same thing.
The DSO formula
DSO = (Accounts receivable ÷ Net credit sales) × Number of days
- Accounts receivable: unpaid customer invoices at the end of the period (or the average for the period, see below).
- Net credit sales: sales made on credit during the period, minus returns, credit notes and allowances. Leave out sales paid on the spot.
- Number of days: the length of the period: 30 or 31 for a month, 90 or 91 for a quarter, 365 for a year.
Keep the period consistent. Monthly DSO swings more; quarterly or rolling three-month DSO is usually easier to read.
How to calculate DSO: worked examples
Example 1: quarterly DSO using ending receivables
| Input | Figure |
|---|---|
| Credit sales, July to September (92 days) | $270,000 |
| Accounts receivable on 30 September | $108,000 |
DSO = $108,000 ÷ $270,000 × 92 = 0.40 × 92 = 36.8 days. Many businesses simplify a quarter to 90 days, which gives 36.0 days. Either is fine as long as you use the same convention every time.
Example 2: using average receivables
Ending balances can be distorted by a big invoice raised on the last day. Averaging the opening and closing balance smooths that out. If receivables were $96,000 on 1 July and $108,000 on 30 September, the average is ($96,000 + $108,000) ÷ 2 = $102,000.
DSO = $102,000 ÷ $270,000 × 90 = 34.0 days.
Example 3: annual DSO
Annual credit sales of $1,200,000 and year-end receivables of $150,000 give DSO = $150,000 ÷ $1,200,000 × 365 = 45.6 days. Annual DSO is useful for comparing years, but it hides seasonal swings.
The countback method (for seasonal businesses)
The standard formula assumes sales are spread evenly. If sales are lumpy, the countback method is more accurate: you "count back" through recent months of sales until you have accounted for the whole receivables balance.
Say receivables at 31 October are $100,000. October credit sales were $60,000 (31 days) and September's were $50,000 (30 days).
- October's $60,000 covers 31 days. Remaining balance: $100,000 − $60,000 = $40,000.
- The remaining $40,000 is part of September's $50,000: $40,000 ÷ $50,000 × 30 = 24 days.
- Countback DSO = 31 + 24 = 55 days.
Using the simple formula on the October month alone would give $100,000 ÷ $60,000 × 31 = 51.7 days, which understates the problem when sales just rose.
What is a good DSO?
There is no universal target. The most useful benchmark is your own payment terms.
| Your terms | DSO | What it suggests |
|---|---|---|
| Net 30 | 25–35 days | Most customers pay on or near time |
| Net 30 | 36–45 days | A meaningful share pay a week or two late |
| Net 30 | Over 45 days | Late payment is normal; collections need attention |
| Due on receipt | Over 15 days | Terms are not being followed in practice |
These bands are rules of thumb for interpreting your own numbers, not industry statistics. Some sectors routinely work on longer terms (Net 60 or Net 90 with large corporate buyers), so compare like with like. Our guide to invoice payment terms covers what each term means.
Best possible DSO
Best possible DSO uses only receivables that are not yet due: current receivables ÷ credit sales × days. If $60,000 of the $108,000 in Example 1 is not yet due, best possible DSO = $60,000 ÷ $270,000 × 90 = 20 days. The gap between actual DSO (36) and best possible DSO (20), 16 days, is roughly the delay caused by late payment rather than by your terms.
Why DSO matters for cash flow
Every day of DSO is a day of sales you have earned but cannot spend. With $270,000 of credit sales in 90 days, average daily credit sales are $3,000. Cutting DSO from 36 to 26 days releases about 10 × $3,000 = $30,000 of cash, without selling anything extra. That can be the difference between paying suppliers on time and dipping into an overdraft. Our cash flow management guide shows how to plan around it.
DSO is one half of the cash conversion story. The other half is how long you take to pay your own bills, measured as days payable outstanding (DPO). We compare the two sides in accounts payable vs accounts receivable.
DSO vs the aging report
DSO tells you there is a problem; the accounts receivable aging report tells you where. The aging report groups each customer's unpaid invoices into buckets (current, 1–30, 31–60, 61–90 and 90+ days overdue). If DSO jumps, open the aging report and you will usually find one or two large customers in the older buckets. Fix those, and DSO follows.
How to reduce days sales outstanding
- Invoice the same day you deliver. The clock on payment terms starts at the invoice date. A week's delay in invoicing adds a week to DSO.
- Make invoices impossible to misread. Clear due date, PO number, itemized lines and payment details. Our list of common invoice mistakes covers what slows approval.
- Agree terms up front and put them in the contract and on every invoice.
- Make paying easy. Bank details, ACH or a payment link on the invoice itself. See how to add a payment link to an invoice.
- Send reminders on a schedule: before the due date, on it and at set intervals after. Our payment reminder email templates cover each stage.
- Take deposits or milestone payments on large jobs so less is outstanding at any time.
- Consider an early payment discount for customers who can pay quickly, if your margins allow it.
- Review credit limits for customers who are repeatedly late.
- Resolve disputes quickly. A disputed invoice is a stalled invoice. Issue a credit note or correction promptly.
Common DSO calculation mistakes
- Including cash sales. Card or cash payments taken at the time of sale inflate the denominator and flatter DSO.
- Mixing periods. Using a year-end receivables balance with one month's sales produces nonsense.
- Ignoring credit notes. Use net credit sales after returns and credits.
- Comparing gross receivables that include sales tax with sales that exclude it. Be consistent: either include tax in both or neither.
- Reading one month in isolation. Track a rolling trend, ideally on a simple sheet such as the one in our invoice tracker spreadsheet guide.
Tracking DSO in a spreadsheet
A basic monthly tracker needs four columns: month, credit sales, closing receivables and DSO. With credit sales in B2, receivables in C2 and days in the month in D2, the DSO formula is =C2/B2*D2. Add a three-month rolling version once you have a few months of data: total receivables at month-end divided by the last three months' credit sales, times the number of days in those three months.
Next step
Calculate last quarter's DSO with the formula above and compare it with your standard terms. If the gap is more than a week or two, pull an aging report, chase the oldest invoices first, and make sure every new invoice goes out on the day of delivery with a clear due date, for example using the corporate invoice template.
Frequently asked questions
What is days sales outstanding?
Days sales outstanding (DSO) is the average number of days it takes a business to collect payment after making a sale on credit. It is calculated by dividing accounts receivable by credit sales for a period and multiplying by the number of days in that period.
What is a good DSO?
A good DSO is one close to your payment terms. If you invoice on Net 30, a DSO in the low 30s means customers pay roughly on time; a DSO of 50 or 60 means many are paying late. Compare against your own terms and trend rather than a single industry figure.
Should I use total sales or credit sales in the DSO formula?
Use credit sales, meaning sales invoiced for later payment. Cash and card sales paid at the point of sale never become receivables, so including them makes DSO look better than it really is. If you can't separate them, note that your figure is an approximation.
Is a higher or lower DSO better?
Lower is generally better because it means cash comes in sooner. A very low DSO compared with your terms can also mean your credit policy is so strict that you are turning away good customers, so look at it alongside sales growth.
What is the difference between DSO and the aging report?
DSO is a single average number for the whole ledger, useful for tracking trends. An aging report lists each customer's unpaid invoices by how overdue they are, so it tells you who to chase. Use DSO to spot a problem and the aging report to fix it.
What is the difference between DSO and DPO?
DSO measures how long your customers take to pay you; DPO (days payable outstanding) measures how long you take to pay your suppliers. DSO uses accounts receivable and credit sales, while DPO uses accounts payable and purchases or cost of goods sold. A business with a DSO of 45 days and a DPO of 30 days is funding a 15-day gap from its own cash.
What is average days delinquent?
Average days delinquent (ADD) is the gap between your actual DSO and your best possible DSO. It estimates how many days of delay come from customers paying late rather than from your payment terms. If DSO is 36 and best possible DSO is 20, ADD is 16 days. A rising ADD points to a collections problem, while a rising DSO with a flat ADD usually means your terms got longer.
How is DSO related to accounts receivable turnover?
They are two views of the same thing. Accounts receivable turnover is net credit sales divided by average receivables, which shows how many times a year you collect your whole ledger. DSO is the number of days in the period divided by that turnover. An annual turnover of 10 gives a DSO of 365 ÷ 10 = 36.5 days, and a higher turnover always means a lower DSO.
Why does my DSO go up when sales are growing?
Because a batch of new invoices raised near the end of a period swells receivables before customers have had time to pay, while the sales figure is spread over the whole period. DSO can rise even if everyone pays on time. Use average receivables, a rolling three-month figure or the countback method, and check the aging report before concluding that customers have slowed down.
Does invoice factoring lower DSO?
It usually lowers your reported DSO, because invoices sold to a factor leave your accounts receivable. Your customers do not pay any faster, though, and you pay fees for the early cash. Lenders may ask whether DSO fell because of factoring, so note it when you compare periods. Invoice financing that keeps the invoices on your books generally does not change DSO.
Invoice Creator Editorial Team
Guides on invoicing, cash flow and small-business finance from Invoice Creator, operated by Next Software Development Company. Content is reviewed for accuracy against the fields our own invoice generator produces.
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