I am married but have not lived with my spouse for six years. Can I file single?

[sasquith]

We both live in California

[Phillip1]

No. You cannot file single. However, you may be able to file head of household if the following applies:

1. You are unmarried or considered unmarried on the last day of the year. See Marital Status , earlier, and Considered Unmarried , later.

2. You paid more than half the cost of keeping up a home for the year.

3. A qualifying person lived with you in the home for more than half the year (except for temporary absences, such as school). However, if the qualifying person is your dependent parent, he or she doesn't have to live with you. See Special rule for parent , later, under Qualifying Person.

Considered Unmarried

To qualify for head of household status, you must be either unmarried or considered unmarried on the last day of the year. You are considered unmarried on the last day of the tax year if you meet all the following tests.

1. You file a separate return. A separate return includes a return claiming married filing separately, single, or head of household filing status.

2. You paid more than half the cost of keeping up your home for the tax year.

3. Your spouse didn't live in your home during the last 6 months of the tax year. Your spouse is considered to live in your home even if he or she is temporarily absent due to special circumstances. See Temporary absences , later.

4. Your home was the main home of your child, stepchild, or foster child for more than half the year. (See Home of qualifying person , later, for rules applying to a child's birth, death, or temporary absence during the year.)

5. You must be able to claim an exemption for the child. However, you meet this test if you can't claim the exemption only because the noncustodial parent can claim the child using the rules described later in Children of divorced or separated parents (or parents who live apart) under Qualifying Child or in Support Test for Children of Divorced or Separated Parents (or Parents Who Live Apart) under Qualifying Relative. The general rules for claiming an exemption for a dependent are explained later under Exemptions for Dependent

You may disregard the community property income allocation for Married Filing Separate filers if the following applies:

Spouses living apart all year.    If you are married at any time during the calendar year, special rules apply for reporting certain community income. You must meet all the following conditions for these special rules to apply.

1. You and your spouse lived apart all year.
2. You and your spouse did not file a joint return for a tax year beginning or ending in the calendar year.
3. You and/or your spouse had earned income for the calendar year that is community income.
4. You and your spouse have not transferred, directly or indirectly, any of the earned income in condition (3) above between yourselves before the end of the year. Do not take into account transfers satisfying child support obligations or transfers of very small amounts or value.

If all these conditions are met, you and your spouse must report your community income as discussed next. See also Certain community income not treated as community income by one spouse , earlier.

Earned income.    Treat earned income that is not trade or business or partnership income as the income of the spouse who performed the services to earn the income. Earned income is wages, salaries, professional fees, and other pay for personal services.

  Earned income does not include amounts paid by a corporation that are a distribution of earnings and profits rather than a reasonable allowance for personal services rendered.

Trade or business income.    Treat income and related deductions from a trade or business that is not a partnership as those of the spouse carrying on the trade or business.

Partnership income or loss.    Treat income or loss from a trade or business carried on by a partnership as the income or loss of the spouse who is the partner.

Separate property income.    Treat income from the separate property of one spouse as the income of that spouse.

Social security benefits.    Treat social security and equivalent railroad retirement benefits as the income of the spouse who receives the benefits.

Other income.    Treat all other community income, such as dividends, interest, rents, royalties, or gains, as provided under your state's community property law.

[cbrisson]

Item #2 in the qualifications is difficult to comprehend.

"2.  You and your spouse did not file a joint return for a tax year beginning or ending in the calendar year."

Huh?

"...for a tax year beginning or ending in the calendar year."

Can you rephrase this for clarity, please?

[GeorgeM777]

A calendar year is a fixed period of time; however, a tax return may concern any number of years.  For example, many taxpayers will probably file their 2021 tax return in calendar year 2022.  Additionally, some may need to amend a prior year tax return, e.g. 2020 or 2019, and they may file that amended return during calendar year 2022.   And there are some taxpayers who may have never filed a tax return for 2020 or 2019, or an earlier tax year, and decide to file such return during calendar year 2022.  

Thus, the first part of the phrase You and your spouse did not file a joint return for a tax year... relates to any joint return for any tax year. The latter part of the phrase, beginning or ending in the calendar year relates to the period beginning January 31st and ending December 31st.  

@cbrisson