Tax Year

The 12-month period for which you are filing your tax return.

Investopedia Says:
Also known as the calendar year.

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Period that a tax return covers. Taxpayers file on a calendar-year basis unless another accounting period has been chosen. A fiscal-year basis referring to any other one-year interval can also be selected. If a tax year is to be changed, approval must be received from the Internal Revenue Service. A new company or estate may employ any allowable tax year, but a new partnership has to use the same period employed by the major partners.