How do I find the bad debt expense percent when all the info I have is sales, credit sales, collections on accounts receivable, and receivable written off?

Isn't bad debt expense the same as receivables written off? (You might add "collection costs" to that to get bad debt expense). To express bad debt as a percentage, I would divide it by credit sales. The debt writeoffs and credit sales should be for the same or comparable periods of time.

Some banks and investment brokers are having a big problem with this kind of accounting question now, as tens of billions of dollars in bad debts are being written off.