How do you account for a provision (allowance) for doubtful debts affecting receivables?

A provision for doubtful debts estimates receivables that may not be collected without writing off specific accounts. Create/increase it by debiting the doubtful debts expense and crediting the allowance (a contra to receivables); reduce it with the reverse entry. Net receivables shown = gross receivables less the allowance.

Create 400 allowance: Dr Doubtful Debts Expense 400; Cr Allowance for Doubtful Debts 400.