Yes there is. The first step of the rule is custodial or domiciliary parent wins unless there is a court order AND a signed 8332 on file. If there is no legally ordered shared custody arrangement then the parent the child lived with the majority of the time wins. Unless you are talking about a leap year, like last year, someone had the child at least one more night then the other. Assuming neither of those tests applies, like in the case of urn married parents living together, then the parent with the higher adjusted gross income wins. This is for dependency status. Similar, yet slightly different, rules apply for head of household status and earned income credit.