The calendar year runs from January 1 to December 1 of every year, but a fiscal year may start on the first day of any month except January. The fiscal year is any 12 consecutive months chosen to be the official accounting period by a business or organization.
Another term for fiscal year is financial year. The tax year is a 12-month accounting period for which income and expenses are recorded for taxation. Usually the tax year is the same as the calendar year in the United States, but the Internal Revenue Service makes exceptions if there is a good reason.