A person's filing status determines which tax rates and which standard deduction amounts apply to a specific tax return. This determination is mostly affected by what that person's marital status is on the last day of the year. If you are married on the last day of the year, you are considered married for tax purposes for that year. If you are not married on the last day of the year, you are considered not married for tax purposes for that year. There are special situations where married persons can be "considered unmarried" for purposes of qualifying for the head of household status even if they are not legally divorced or separated.