Accounts payable days, usually called days payable outstanding, expresses what you owe as a number of days of purchases. It is a genuinely useful figure and it is misread more often than almost any other number in a small business, because it is treated as a performance measure when it is mostly a description of policy. A high DPO can mean you have negotiated good terms and are using them, or that you are paying late and damaging supplier relationships. The number alone does not distinguish those, and that is why it is read alongside the overdue share rather than on its own. This page is the calculation, what moves it, and how to read it honestly.
The calculation, and the approximation in it
Payables divided by purchases on credit, times the days in the period. On the worked example on this site, $48,000 current, $21,000 at thirty days, $9,500 at sixty and $4,200 beyond is $82,700 owed, 42% of it overdue, with days payable outstanding of 30.26. Most small businesses approximate purchases with cost of sales, which is close enough for a trend and wrong enough that comparing with somebody who did it differently is meaningless.
What moves it
The terms you negotiated, whether you use them, your purchasing pattern, and the point in the month you measure. That last one catches people out: DPO measured the day after a payment run is a different number from the day before, and neither is wrong.
Reading it honestly, beside the overdue share
High DPO with a low overdue share is terms being used as intended. High DPO with a high overdue share is paying late. The two readings call for opposite responses, and the DPO figure alone cannot tell you which you are looking at.
Questions people ask about accounts payable days
What is a good DPO?
Not a question we will answer with a number. It depends on your industry, your negotiated terms and your cost of cash, and a benchmark applied to the wrong business is worse than no benchmark. Watch your own trend.
Should we deliberately increase DPO?
It is a treasury decision with a supplier-relationship cost, and it should be made deliberately by whoever owns that relationship rather than as a by-product of a payables target.
Does DPO belong in the management accounts?
Alongside the overdue share, yes. On its own it invites exactly the misreading described above.