Understanding Days Past Due
Days past due is the number of days since an obligation's due date passed without it being settled. It is the backbone of every aging report and the default sort order of every collections queue.
It is also computed carelessly in most systems, in ways that systematically understate the problem.
The first lie: blending per account
Many systems compute DPD against an account balance rather than per obligation. An account with a two-year-old unpaid assessment and a recent monthly charge shows a small DPD, because the recent charge dilutes it.
Aging must be per obligation. An account then has several ages, and the oldest is the one that matters — the two-year-old item does not become less serious because something newer was paid.
The second lie: resetting on payment
If a partial payment resets the clock, a payer can stay permanently current on a balance they have owed for a year by paying a token amount each month.
The obligation's age should run from its own due date regardless of partial settlement. What changes with a partial payment is the outstanding amount, not the age.
The third lie: ignoring grace
DPD measured from the due date and 'overdue' are not the same thing. An account four days past due inside a fourteen-day grace period is not overdue, and reporting it as such produces reminders that damage relationships and a queue nobody trusts.
Report both: days past due as the raw measure, and standing as the interpretation.
What DPD cannot tell you
Even computed correctly, DPD is a measure of time, not of collectability. An account at 62 days with a kept promise due today is more likely to pay than one at 31 days that has never responded.
This is why sorting a worklist purely by DPD produces a queue that feels arbitrary to the people working it. Use it as one input alongside standing, promise history, value and reachability.