How is bad debt expense calculated when the aging of accounts receivable method is used?

1) Bad debt expense is calculated directly as the sum of uncollectible amounts based on the age of the account.

2) Bad debt expense is calculated as the sum of uncollectible amounts based on the age of the account balance less the current outstanding balance in the allowance for doubtful accounts.

3) Bad debt expense is calculated as the sum of uncollectible amounts based on the age of the account balance plus the current outstanding balance in the allowance for doubtful accounts.

4) None of the above