Castle Company provides estimates for its uncollectible accounts. The allowance for uncollectible accounts had a credit balance of $18,130 at the beginning of 2021 and a $24,110 credit balance at the end of 2021 (after adjusting entries). If the direct write-off method had been used to account for uncollectible accounts (bad debt expense equals actual write-offs), the income statement for 2021 would have included bad debt expense of $18,800 and revenue of $3,900 from the collection of previously written off bad debts.

Determine bad debt expense for 2021 according to the allowance method.