A contra asset account is an asset account where the balance will be either a credit balance or a zero balance. (A debit balance in a contra asset account will violate the cost principle.) Since a credit balance in an asset account is contrary to the normal or expected debit balance the account is referred to as a contra asset account.
The most common contra asset account is Accumulated Depreciation. Accumulated Depreciation is associated with property, plant and equipment and it is credited when Depreciation Expense is recorded. Recording the credits in the Accumulated Depreciation means that the cost of the property, plant and equipment will continue to be reported. Reporting the accumulated depreciation separately allows the readers of the balance sheet to see how much of the cost has been depreciated and how much has not yet been depreciated.
Another contra asset account is Allowance for Doubtful Accounts. This account appears next to the current asset Accounts Receivable. The account Allowance for Doubtful Account is credited when a company enters estimated amounts as debits to Bad Debts Expense under the allowance method. The use of Allowance for Doubtful Accounts permits a reader to see the documented amounts in Accounts Receivable that the company has a right to collect from its credit customers. The separate credit balance in the account Allowance for Doubtful Accounts tells the reader how much of the debit balance in Accounts Receivable is unlikely to be collected.
A less common example of a contra asset account is Discount on Notes Receivable. The credit balance in this account is amortized or allocated to Interest Income or Interest Revenue over the life of a note receivable.