What is a tax year?

A tax year is the 12 months used for calculating and reporting taxes, either following the calendar year (January through December) or a fiscal year ending on the last day of any month except December. For professional service firms, the tax year determines filing deadlines and planning cycles.

Key characteristics

• 12-month reporting period

• Calendar or fiscal year

• Determines filing deadlines

• Once chosen, it's hard to change

• Most small businesses use a calendar

• Affects estimated tax timing

Why it matters for professional service firms

The tax year structures your entire financial and compliance calendar. Calendar years simplify coordination with personal returns and industry norms. Professional service firms typically use calendar years unless specific circumstances favor a fiscal year.

Real-world example

Patricia's S Corp used a calendar tax year (January through December). Tax calendar: quarterly estimates due April 15, June 15, September 15, January 15; S corp return due March 15; personal return due April 15. Calendar year-aligned business and personal planning. Considered the fiscal year for seasonal business, but calendar simplicity won.