A write-off may refer to either an accounting write-off or an income tax write-off. It is also a term commonly used in vehicle insurance to describe a vehicle which is cheaper to replace than to repair, known in the U.S. as being a totaled car. 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 $49,9… (More on Write-off)