Generally, your marital status on the last day of the year determines your status for the entire year. If you are unmarried, or if you are legally separated from your spouse under a divorce or separate maintenance decree according to your state law, and you do not qualify for another filing status, your filing status is single.
Generally, to qualify for head of household status, you must be unmarried and not entitled to file as a qualifying widow(er) with a dependent child. You must also have provided more than half the cost of maintaining as your home a household that was the main home for a qualifying person. You may also qualify for head of household status if you, though married, file a separate return, your spouse has not lived in your home during the last six months of the tax year, and you provided more than half the cost of maintaining as your home a household that was the main home for a qualifying child for more than one half of your tax year.
If you are married, you and your spouse may file a joint return or separate returns.
If your spouse died in the previous tax year and you did not remarry before the end of the current tax year, you may still file a joint return. This is the last year for which you may file a joint return with that spouse.
If your spouse died during one of the 2 previous tax year, you may be able to file as a qualifying widow or widower. To do this, you must meet all four of the following tests:
- You were entitled to file a joint return with your spouse in the year he or she died. It does not matter whether you actually filed a joint return,
- You did not remarry before the end of the tax year,
- You have a child, stepchild, adopted child, or foster child for whom you can claim a dependency exemption, and
- You paid more than half the cost of keeping up a home that was the main home for you and that child, for the whole year
https://www.irs.gov/help/ita/what-is-my-filing-status