You disbursed a ₦100,000 loan with a 30-day repayment. Day 30 passes, the user hasn't paid. Day 31, day 45, day 60, day 91. Each milestone moves the loan into a new DPD (Days Past Due) bucket and triggers a different impairment treatment. Under IFRS 9 (and CBN's prudential guidelines), a 30-day-overdue loan is Stage 2 (significant deterioration, lifetime ECL); a 90-day-overdue loan is Stage 3 (default, full ECL with interest unwinding). The classification drives the provision your CFO has to book. This lesson posts a single loan through the DPD lifecycle so you see why your loan-book report needs a `bucket_at_close` column that auto-recomputes nightly.