Move receivables into older buckets and watch the allowance and bad debts expense recompute.
| Age | Balance | Rate | Uncollectible |
|---|---|---|---|
| Not yet due | $100,000 | 1% | $1,000 |
| 1–30 days past due | $0 | 3% | $0 |
| 31–60 days past due | $0 | 10% | $0 |
| 61–90 days past due | $0 | 25% | $0 |
| Over 90 days past due | $0 | 50% | $0 |
| Total | $100,000 | $1,000 |
$1,000
$350
sorts every account by how overdue it is, and applies a higher uncollectible rate the older it gets. The total is not an expense — it is the balance the must reach.
The expense is whatever closes the gap between that target and what the allowance already holds. A leftover credit balance shrinks the entry; a leftover debit balance, from writing off more than expected, makes it bigger.