A fiscal year is the twelve-month period that a company or government uses for accounting purposes and preparing financial statements. The fiscal year may or may not be the same as a calendar year. For tax purposes, companies can choose to be calendar-year taxpayers or fiscal-year taxpayers. The default IRS system is based on the calendar year, so choosing a fiscal year-end other than December 31 means that a taxpayer has to make some adjustments to the deadlines for filing certain forms and making certain payments. The vast majority of companies choose December 31 as the fiscal year end and if you want to use a different date, be sure to check with tax and accounting advisors.