The term write-off describes a reduction in recognized value. In accounting terminology, it refers to recognition of the reduced or zero value of an asset. In income tax statements, it refers to a reduction of taxable income as recognition of certain expenses required to produce the income. Write-off is also used in vehicle insurance to describe a vehicle which is cheaper to replace than to repair, sometimes colloquially referred to as being "totaled" (a total loss).
Income tax
In income tax calculation, a write-off is the itemized deduction of an item’s value from one’s taxable income. Thus, if a person has a taxable income of $50,000 per year, a $100 telephone for business use would lower the taxable income to $49,900. If that person is in a 25% tax bracket, the tax due would be lowered from $7,481 to $7,456. Thus the net cost of the telephone is $75 instead of $100.
More accurately no income taxes would be due on the expense/write off. So the net benefit would still be $25 in reduction to the taxes owed. However 25% of $50,000(taxable income) would be $12,500 and the reduction to $49,900(taxable income) would result in taxes due of $12,475 ($25 less).
Accounting
In business accounting, the term write-off is used to refer to an investment (such as a purchase of salable goods) for which a return on the investment is now impossible or unlikely. The item’s potential return is thus canceled and removed from ("written off") the business’s balance sheet. Common write-offs in retail include spoiled and damaged goods.
Banking
Similarly, banks write off bad debt that is declared noncollectable (such as a loan on a defunct business or a credit card due that is now in default), removing it from their balance sheets.
Negative write-offs
A negative write-off refers to the decision not to pay back an individual or organization that has overpaid on an account. Negative write-offs can sometimes be seen as fraudulent activity if those who overpay a claim or bill are not informed that they have overpaid and are not given any chance to reconcile their overpayment or be refunded.
Some institutions such as banks, hospitals, universities, and other large organizations regularly perform negative write-offs, especially when the amount is considered low dollar, e.g. $5.00 at some places or up to $15.00 or more at others
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