Accounting for impaired assets
Let's get into the nitty-gritty of asset impairment, starting with how to calculate it.
For ARs, it's pretty easy. If a client defaults, the business can write off the amount of their account. If a business has several accounts going bad at once because of an economic calamity, it can adjust the rate that it uses for bad debt expense to proactively write off more. The same is generally true for fixed assets. There may be unique instances where a fixed asset is impaired prior to its sale or disposal, but, for the most part, the business knows exactly the amount of the impairment because there's an actual transaction record.
Loans are tougher, and process that banks use to write off loans would take an entire textbook to explain. Banks have several risk levels for loans, and they're moved to higher risk levels as the payments are missed or paid late. If a loan is officially restructured with the client or the client defaults, it's totally or partially written off. Otherwise, the bank keeps an allowance account for loan losses based on historical losses but doesn't write off individual loans until forced to do so.