What does days delinquent mean on an invoice?

Days delinquent tells you how far a single invoice has drifted past its terms. An invoice on net-30 terms that is 45 days old is 15 days delinquent. The number matters because different collection approaches apply at different thresholds: a gentle reminder at day 3, a direct call by day 14, a formal notice approaching day 60.

Days delinquent is distinct from DSO, which is an average across the entire AR book. A business can have a healthy aggregate DSO of 35 days while still carrying a few invoices with individual delinquency counts of 90 or more. Reviewing the tail of the aging report — the invoices with the highest individual days-delinquent figures — is a separate exercise from tracking DSO and often reveals the accounts most in need of direct attention.