ADD separates late payment from payment terms. If you give a large customer 60-day terms instead of 30, DSO goes up even when that customer pays on the due date, while ADD does not move. Some credit teams call it delinquent DSO, and it is usually reported monthly next to days sales outstanding.
Average days delinquent formula
Average days delinquent = DSO minus best possible DSO
Both parts use the same credit sales and the same number of days. DSO divides total receivables by credit sales for the period and multiplies by its days. Best possible DSO does the same with current receivables only, the invoices that are not yet due, so it shows the DSO you would have if every customer paid on time.
Because the two parts share a denominator, the formula shortens to past-due receivables divided by average daily credit sales. ADD tells you how many days of sales are sitting in overdue invoices.
How to calculate average days delinquent
Example. In September, a 30-day month, a wholesaler issues $1,200,000 of invoices on credit, or $40,000 a day. On September 30 its aging report shows $2,000,000 of receivables, of which $1,400,000 is current and $600,000 past due. All figures are illustrative.
- DSO is $2,000,000 ÷ $1,200,000 × 30 = 50 days.
- Best possible DSO is $1,400,000 ÷ $1,200,000 × 30 = 35 days.
- ADD is 50 minus 35 = 15 days.
The shortcut gives the same answer, $600,000 ÷ $40,000 = 15 days. Of the wholesaler's 50 days of DSO, 35 are invoices that are not yet due and 15 are late payment.
Why the same DSO can hide a different ADD
Two companies with the same DSO can have very different collection problems. The table compares two illustrative companies at the end of a 30-day month, each with credit sales of $1,200,000.
| Measure | Company A | Company B |
|---|---|---|
| Payment terms | 45 days | 30 days |
| Total receivables | $2,000,000 | $2,000,000 |
| Current receivables | $1,800,000 | $1,200,000 |
| DSO | 50 days | 50 days |
| Best possible DSO | 45 days | 30 days |
| ADD | 5 days | 20 days |
Company A's DSO comes mostly from long terms, and its customers pay close to the due date. Company B's customers pay about 20 days late, which points to a collections problem rather than long terms. DSO alone would rank the two the same.
How to read average days delinquent
An ADD of zero means nothing was past due at the end of the period. Track it monthly and watch the trend, because a rising ADD means customers are paying later, whatever happens to sales or terms.
ADD measures the past-due balance in days of sales, which is different from the age of each overdue invoice. It works best when sales are steady, because a spike in sales near the period end raises average daily sales and pulls ADD down. One large invoice a few days late can also weigh as much as many small ones months late, so check the accounts receivable aging report to see which customers make up the past-due balance.
The collection effectiveness index uses the same past-due balance in a different way. It shows what share of the money you could have collected came in, while ADD shows how many days of sales are still overdue.
Sunbay connects to your ERP or accounting system and reports DSO and receivables aging, the totals behind both parts of ADD. It matches incoming payments using ERP data, so paid invoices do not inflate the past-due balance, and it flags invoices it predicts will be paid late. Reminders by email and SMS and AI voice calls run on overdue invoices, and every customer reply stays next to the invoice, which helps explain a month when ADD rises. See how Sunbay reports DSO and aging.
Frequently asked questions
How do you calculate average days delinquent?
Subtract best possible DSO from DSO. With DSO of 50 days and best possible DSO of 35, ADD is 15 days, the same as dividing past-due receivables by average daily credit sales.
What is best possible DSO?
It is the DSO you would have if no invoice were overdue. Divide current receivables by credit sales for the period and multiply by the days in it. With steady sales it sits close to your average payment terms.
What is the difference between ADD and DSO?
DSO counts all receivables, so it rises with longer payment terms as well as with late payment. ADD counts only the past-due part, so it measures late payment alone.
What is a good average days delinquent?
As close to zero as you can get, since each day of ADD is a day of sales that fell due and has not been paid. There is no official benchmark, so compare it with your own history and look into any month where it jumps.
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