Termination of a marriage can have a major impact on a couple's taxes, whether you have filed for a divorce or a legal separation. There are, however, some legal details you should be aware of. These are outlined below:

The marital status of spouses is terminated when the couple is legally separated under a decree of divorce or of separate maintenance (Code Sec. 2(b)(2), Code Sec. 7703(a)(2), Code Sec. 6013(d)(2)). 

This termination of the marital status for tax purposes is constitutional (Hamilton, Raleigh, (1977) 68 TC 603). An interlocutory (temporary) decree of divorce doesn't end a marriage until the decree becomes final (Reg § 1.6013-4(a), Rev Rul 57-368, 1957-2 CB 896).  A couple living under a legal separation agreement but without any court decree isn't legally separated for tax purposes because such an agreement could be abrogated by the parties upon reconciliation and resumption of cohabitation.