Calculate days sales outstanding (DSO) for your business
DSO tells you how many days it takes, on average, to get paid after you've sent an invoice. If your DSO is 45, that means it's taking your customers about 45 days to pay you.
That number matters because it directly affects your cash flow. The higher your DSO, the longer your cash sits in someone else's account. And the harder it gets to forecast what you'll actually have on hand next month.
You can run the calculation for any period you want, whether that's a month, a quarter, or a full year. Just make sure you match the accounts receivable balance and credit sales to the same time window.
Why listen to us
We built Lunos to help finance teams collect cash faster without adding headcount. Ramya Varma, CFO at Workweek, reduced her DSO from around 46 days to about 36 after bringing Lunos into her AR process. That's exactly the kind of improvement this calculator helps you measure.
How to use this DSO calculator
You'll need three numbers to run the calculation, and all of them come from your accounting system or ERP.
Accounts receivable balance is the total amount your customers currently owe you. In most systems, you'll find this on your balance sheet or in your AR aging report. If you're calculating for a specific period, use the AR balance at the end of that period.
Total credit sales is the revenue you generated on credit during the same period. This doesn't include cash sales or prepayments. Pull this from your income statement, and make sure it covers the same time window as your AR balance. If your system doesn't separate credit sales from total revenue, use net revenue as a close approximation, since most B2B companies sell primarily on credit terms.
Days in period depends on the window you're measuring. Use 30 for a month, 90 for a quarter, or 365 for a full year. Shorter periods give you a more current snapshot. Annual figures won't catch seasonal swings as well, but they're better for year-over-year comparisons.
Toggle between DSO and average collection period mode to see both metrics. They use the same formula and produce the same result, but "average collection period" is the term you'll see more often in banking and credit analysis.
The DSO formula explained
The formula's straightforward.
DSO = (Accounts Receivable / Total Credit Sales) x Days in Period
You divide your AR balance by total credit sales for the period, then multiply by the number of days. That'll tell you how many days, on average, your invoices stay unpaid.
One question that comes up a lot is whether you should use average AR or period-end AR. Average AR (the beginning balance plus the ending balance, divided by two) gives a smoother picture when your receivables fluctuate during the period. Period-end AR is simpler and most analysts use it when the difference isn't material.
The same goes for credit sales versus total revenue. Technically, you'd use credit sales only, since cash sales get collected right away. But public companies rarely separate the two in their reporting, so total net revenue's the standard proxy.
DSO worked example
Say your business has $150,000 in accounts receivable at the end of the quarter. Your total credit sales for that quarter were $500,000, and the quarter was 90 days long.
Plug those numbers into the formula.
DSO = ($150,000 / $500,000) x 90 = 27 days
That means your customers pay you in 27 days on average. If your payment terms are net 30, you're in good shape, since your customers are paying before the due date.
Now switch the calculator to average collection period mode. You get the same number, 27 days, because the underlying math is identical. It's the same math, just a different label depending on which team you're talking to.
DSO vs average collection period
These two metrics use the same formula and give you the same result. The difference is context.
"Days sales outstanding" is the term you'll hear most in finance and AR teams. It's the standard metric for tracking how efficiently a company collects its receivables.
"Average collection period" shows up more in credit analysis and banking. Lenders and credit analysts use it to gauge how quickly a business turns sales into cash, especially when they're assessing credit risk.
If someone asks you for one but you've calculated the other, you already have the answer. They're the same number.
What is a good DSO? Benchmarks by industry
A DSO under 45 days is generally considered healthy for most B2B businesses. But what's actually healthy for you depends on your industry and your own payment terms.
The Credit Research Foundation's Q4 2025 domestic trade receivables summary reported a broad median DSO of 40.5 days across all industries. But that median doesn't tell the full story. Here are benchmarks by sector, based on NYU Stern Damodaran's January 2026 working capital data:
The most useful comparison isn't your DSO against a generic benchmark. It's your DSO against your own payment terms. Say your standard terms are net 30 and your DSO is 52. That means your customers are paying 22 days late on average, and that gap is where cash gets stuck.
What is a good DSO for a small business?
For small businesses, a DSO between 30 and 45 days is a solid target. Anything under your stated payment terms means they're paying on time.
Small businesses feel the impact of a high DSO more than large enterprises. They don't usually have the cash reserves or credit lines to absorb the gap. A DSO that creeps from 35 to 55 over two quarters can put real pressure on payroll and vendor payments, even when revenue is growing.
How to calculate DSO in Excel
If you'd like to track DSO over time without a dedicated tool, a simple Excel setup does the job.
Set up three columns. In cell A1, enter your accounts receivable balance. In B1, enter your total credit sales. In C1, enter the number of days in your period.
In cell D1, enter the formula:
=(A1/B1)*C1
In this example, DSO jumped from 27 to 35 days in Q3 even though revenue grew. That's a signal that collections slowed, and it's worth digging into which customers or invoices are aging.
Regular DSO vs count-back DSO
The formula above is what's known as "regular" or "simple" DSO. It divides your total AR by total sales and multiplies by the period length. It's the most common method, and for businesses with fairly steady revenue, it works well.
Count-back DSO takes a different approach. Instead of dividing totals, you start with your ending AR balance and subtract each month's sales backward until it's fully accounted for. The number of days you "count back" through is your DSO.
Count-back is more accurate for businesses with seasonal revenue or big month-to-month swings. It reflects your actual recent sales pattern rather than an average. But it requires monthly data and a more complex calculation. So most teams start with regular DSO and only switch to count-back when they notice revenue spikes are distorting their numbers.
The fastest levers to reduce DSO
Not all collection improvements show up in your numbers at the same speed. These are ranked by how quickly they tend to reduce your DSO.
Send invoices on the day you deliver. If you're a week late sending an invoice, you're a week late getting paid. It's the simplest fix and it'll show up in your next DSO calculation.
Automate payment reminders before the due date. A reminder at day 25 of a net-30 term catches the invoices that would otherwise slip past the due date and into aging. You'll see less overdue AR within a single billing cycle.
Offer early payment incentives. A 2% discount for paying within 10 days (2/10 net 30) can pull forward a meaningful chunk of your receivables. This works especially well for customers who have the cash but no reason to pay early.
Follow up on overdue invoices immediately, not at month-end. The longer an invoice ages past its due date, the harder it'll be to collect. You'll see a measurable difference by following up on day 31 instead of day 60.
Tighten credit terms for slow-paying customers. Review your AR aging report and shorten terms or require deposits for accounts that won't pay on time.
Automate your collections workflow. Manual follow-ups depend on your team's bandwidth, so they'll drop off when things get busy. Lunos reads customer replies, tracks payment promises, and sends follow-ups automatically, so nothing falls through the cracks. See how it works.
