Normally, taxpayers who remain married as of the end of a taxable year are considered "married" for federal income tax purposes. However, if a taxpayer is legally separated pursuant to a separate maintenance decree then the taxpayer may be considered "unmarried" for federal income tax purposes (so one may claim to be single on one's Form 1040). See IRS Publication 501 for more details (link provided below). This is important because you will want to avoid being held responsible for your spouse's tax liabilities while you remain married (even if New Jersey is not a community property state). Consider having the spousal support order modified to read that you are both legally separated and allowed to claim "single" status for income tax purposes. Alternatively, you can also file as (a) "married filing separately" which will subject you to the same tax rates as an individual taxpayer, or (b) "head of household" if you claim at least one dependent.
I am not familiar with New Jersey divorce law, but a quick search for legal separation in New Jersey indicates that New Jersey does not recognize legal separations. It does appear, however, that New Jersey recognizes a procedure called "limited divorce" that amounts to an economic divorce even though you are still considered legally married to your ex spouse. Consider getting a complete divorce from your ex as the issues that you raise can only cause complications that will become more expensive to untangle as time passes.
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If you are married on the last day of the year you have to file married jointly or married finling separately. In some cases you can flie head of household. If you file married filing separately you can choose whether to take the standard deduction or itemize.
I strongly recommend you speaking with an accountant on this issue to make sure you file correctly and in the most beneficial way for your circumstances.
This answer does not constitute the establishment of an attorney/client relationship nor is there any guarantee that this advice will be completely effective in a court of law. A consultation, including review of court orders and other documents is necessary in order for me to give you proper advice and guidance.
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