DSO calculator and formula
Find your days sales outstanding, how far it runs past your payment terms, and how much cash you’d free up by bringing it down. No signup.
- Days beyond terms
- 12 days
- Each day of DSO is worth
- $100,000
- Cash freed at 35-day DSO
- $700,000
- Yearly cost of carrying that cash
- $56,000
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How DSO is calculated
Days sales outstanding is the average number of days it takes to collect a dollar of credit sales:
DSO = accounts receivable ÷ credit sales × days in the period
The example above uses $4.2M in receivables and $9M of credit sales over the last 90 days. That’s $100,000 of sales a day, so $4.2M of receivables is 42 days of sales still waiting to be collected.
Monthly, quarterly, and annual DSO
The formula is the same for any period. Only the sales figure and the day count change, and they have to cover the same stretch of time.
| Period | Formula | Example |
|---|---|---|
| Monthly | AR ÷ the month’s credit sales × 30 | $4.2M ÷ $3.3M × 30 = 38.2 days |
| Quarterly | AR ÷ the quarter’s credit sales × 90 | $4.2M ÷ $9M × 90 = 42 days |
| Annual | AR ÷ the year’s credit sales × 365 | $4.2M ÷ $36M × 365 = 42.6 days |
The three answers differ because each one averages sales over a different window. A monthly figure reacts quickly to a strong or weak month. An annual figure is steady but slow to show a change. Pick one period and use it every time you report.
In Excel or Google Sheets, put receivables in B1, credit sales in B2, and days in the period in B3, then use =B1/B2*B3.
Average receivables instead of ending receivables
Some teams use average receivables, (opening AR + closing AR) ÷ 2, in place of the ending balance. It keeps one large invoice issued on the last day of the period from inflating DSO. Either version works if you use it consistently.
The countback method
The standard formula assumes sales were spread evenly over the period. When sales are growing or seasonal, the countback method is more accurate. Start with today’s receivables and subtract each month’s credit sales, working backward, until the balance runs out:
- Receivables are $4.2M. September sales were $3.3M, so September counts in full: 30 days, $0.9M left.
- August sales were $3.0M. The remaining $0.9M covers 0.9 ÷ 3.0 of August’s 31 days: 9.3 days.
- Countback DSO is 30 + 9.3 = 39.3 days.
The standard formula gives 42 days for the same quarter, because July’s lower sales pull the daily average down. Countback shows that customers are paying faster than the standard figure suggests.
Best possible DSO and average days delinquent
Best possible DSO uses only the receivables that are not yet due:
Best possible DSO = current receivables ÷ credit sales × days in the period
It is the DSO you would have if every customer paid on the due date. Subtract it from your actual DSO to get average days delinquent (ADD), the number of days customers are paying late on average. If DSO is 42 and best possible DSO is 28, ADD is 14 days. ADD is the part of DSO your collections process controls.
How to read your result
Compare DSO with your payment terms, not with other companies. If you invoice on net 30 and DSO is 42, the average dollar arrives 12 days late. Your terms set a floor you can’t go below without changing them. The days above that floor are the ones your team can win back.
Each of those days is worth one day of credit sales. In the example, going from 42 to 35 days releases $700,000. That’s a one-time release of cash from receivables, not a recurring saving. The yearly figure is what carrying that balance costs you at your cost of capital.
Why DSO runs above terms
In B2B, late payment is rarely a customer deciding not to pay. More often the invoice is stuck somewhere:
- An approval is waiting on someone who’s out, or the AP contact has left.
- The customer’s AP portal rejected the invoice, often for a missing PO number, and nobody saw it. More on AP portals.
- The customer paid less than the invoice, and the difference was never researched. More on short-pays.
- A promised payment didn’t arrive, and there was no follow-up. More on collections.
Scheduled reminder emails don’t fix any of these. If you want to see which ones are behind your number, pull your aging report and sort the oldest balances by the reason they’re stuck. Our payment reminder and collections email templates cover the most common ones.
What this calculator doesn’t account for
- Seasonality. A big month at the end of the period pushes receivables up and makes DSO look worse than it is. Use the last 90 days, or compare the same period year over year.
- The mix of customers. One large account on long terms can move the whole number. For a truer view, calculate DSO separately for your biggest customers.
- Why balances are late. DSO tells you how much is late, not why. Your aging report and the email threads behind it tell you why.
Questions
What is the DSO formula?
DSO = accounts receivable ÷ credit sales for the period × days in the period. With $4.2M in receivables and $9M of credit sales over the last 90 days, DSO is 4.2 ÷ 9 × 90 = 42 days. It is the average number of days it takes to collect a dollar of credit sales.
What is the annual DSO formula?
Annual DSO = accounts receivable ÷ annual credit sales × 365. For a single month, use that month’s credit sales and the number of days in the month (or 30). For a quarter, use the quarter’s credit sales and 90 or 91 days. Keep the period consistent from one calculation to the next.
How do you calculate DSO in Excel?
Put accounts receivable in B1, credit sales for the period in B2, and the number of days in the period in B3, then use =B1/B2*B3. For a monthly trend, put one row per month and copy the formula down.
What is the countback method for DSO?
The countback method works backward from the most recent month. Subtract each month’s credit sales from the receivables balance, counting that month’s days in full, until the balance runs out, then add the fraction of the last month needed to cover what is left. It gives a more accurate DSO when sales are growing, shrinking, or seasonal.
What is best possible DSO?
Best possible DSO = current (not yet due) receivables ÷ credit sales × days in the period. It is what DSO would be if every customer paid exactly on time. The gap between DSO and best possible DSO is called average days delinquent, and it measures how late customers actually pay.
What is a good DSO?
There's no single good number, because it depends on the payment terms you offer. Compare DSO with your terms instead. On net 30 terms, a DSO of 34 means customers pay close to on time. A DSO of 55 means the average dollar arrives more than three weeks late. The gap between DSO and terms is the part your team can change.
Should I use total sales or credit sales?
Credit sales. Cash sales never sit in receivables, so including them makes DSO look better than it is. Most B2B companies invoice almost everything, so for them total revenue is a close stand-in.
Should I use ending or average accounts receivable?
Either works if you're consistent. Ending AR shows where you are today. Average AR (opening plus closing, divided by two) smooths out a large invoice landing on the last day of the period. If your sales swing a lot month to month, use a shorter period, such as the last 30 or 90 days, so DSO reflects recent sales.
What does cash freed mean?
It's the receivables balance you would no longer carry if customers paid at your target DSO, at your current sales level. Each day of DSO is worth one day of credit sales. It's a one-time release of cash, not recurring savings.
Is my data stored?
No. The calculator runs entirely in your browser. Nothing you type is sent to Alder or stored.
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