Normally, the IRS only allows the custodial parent to claim a dependent and all child-related tax credits and only one parent includes the child on his or her tax return. However, there's a special rule for divorced parents or married parents (who lived apart) for the entire last six months of the tax year. 

With this rule: The custodial parent allows the non-custodial parent to claim the child and the tax benefits are split between them as follows:

• Non-Custodial Parent: Claims the child as a non-dependent to claim the head of household filing status, earned income credit and child and dependent care credit (if qualifying). 
• Custodial Parent: Claims the child as a dependent and the child tax credit (if qualifying).

Please view page 10, IRS Publication 504, for more information about this rule.

https://www.irs.gov/pub/irs-pdf/p504.pdf