Income tax systems generally allow a tax deduction for various items, especially expenses incurred to produce income. Often these deductions are subject to limitations or conditions. Tax deductions generally are allowed only for expenses incurred that produce current benefits, and capitalization of items producing future benefit is required, sometimes with exceptions. Most systems allow recovery in some manner over a period of time of capitalized business and investment items, such as through allowances for depreciation, obsolescence, or decline in value. Many systems reduce taxable income for personal allowances or provide a range of income subject to zero tax. In addition, some systems allow deductions from the tax base for items the tax levying government desires to encourage. Some systems distinguish among types of deductions (business versus non-business).

Some systems also refer to withholding tax or withholding of tax from income as a tax deduction. In addition, some systems grant a direct reduction of income tax for certain items, which are usually referred to as tax credits. Neither of these items are not discussed herein.

Business expenses

Nearly all jurisdictions that tax business income allow tax deductions for expenses incurred in trading or carrying on the trade or business. Technical details of the allowance vary, and may be very general or very specific. The amount of particular deductions may be limited based on character or amount, or deductions in aggregate may be limited or reduced.

• Electronic Sales and Use Tax, Inc.
  efilesalestax.com
  Sales Tax filing software for California and Florida.
• Avalara Sales Tax Software
  avalara.com
  State sales tax and use tax calculator for tax calculation, and address verification and validation for accounting software, such as Great Plains, ACCPAC, MAS 90 and MAS 200.
• Kamp Data DynamicZip
  kampdata.com
  Provides sales tax calculations and creates and maintains sales tax schedules for all United States jurisdictions.