Note that if the child lived with you 1 more day than your ex than you will be considered the custodia parent and can claim the child. Here is the details-
Special rule for divorced or separated parents. A child will be treated as the qualifying child or qualifying relative of his or her noncustodial parent if all of the following apply.
Are divorced or legally separated under a decree of divorce or separate maintenance,
Are separated under a written separation agreement, or
Lived apart at all times during the last 6 months of the year.
The child received over half of his or her support for the year from the parents.
The child is in the custody of one or both parents for more than half of the year.
Either of the following applies.
The custodial parent signs a written declaration, discussed later, that he or she will not claim the child as a dependent for the year, and the noncustodial parent attaches this written declaration to his or her return.
Custodial parent and noncustodial parent. The custodial parent is the parent with whom the child lived for the greater part of the year. The other parent is the noncustodial parent.
If the parents divorced or separated during the year and the child lived with both parents before the separation, the custodial parent is the one with whom the child lived for the greater part of the rest of the year.
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Please note: This advice is provided with the understanding that all the relevant facts have been provided by you. Any change in facts might affect the advice given and hence may not be relied on in such cases. Nothing contained in this reply was intended or written to be used, can be used by any taxpayer, or may be relied upon or used by any taxpayer for the purposes of avoiding penalties that may be imposed on the taxpayer under the Internal Revenue Code of 1986, as amended.
You will have to determine if you are custodial parent based on the number of days your daughter stayed with you and with your ex.