My ex and I have a arrangement thru mediation where we alternate claiming our son on taxes. If I keep him for more than 6 months; can she still claim him on her taxes?

[xmasbaby0]

As far as the IRS is concerned, the custodial parent is the one with whom the child spent the most nights--at least 183 nights.  The custodial parent can claim the child as a dependent and file with Head of Household status, get earned income credit and the childcare credit.  IF the custodial parent signs a form 8332 the other parent can get the child tax credit.

If you have some sort if court-ordered agreement about who claims the child, the IRS will not get involved, but it could land you in legal trouble.  Tread carefully.

[Critter]

A court order/agreement cannot contradict IRS rules ... so you will follow the order within the IRS regulations. 

There is no such thing in the Federal tax law as 50/50, split, or joint custody.  The IRS only recognizes physical custody (which parent the child lived with the greater part, but over half, of the tax year.  That parent is the custodial parent; the other parent is the noncustodial parent.)

Who can claim the exemption and credits depends on who is the custodial parent. (By the IRS definition of custodial parent for tax purposes - this is not the same as the legal custody that a court might grant.).

The test that the IRS uses to determine the custodial parent is where the child lived for more than 1/2 (or greater part) of the year. The IRS will go so far as to require counting the nights spend in each household - that person is the custodial parent for tax purposes (if exactly equal and more than 183 days - The custodial parent is the parent with the highest AGI, if less than 183 days then neither parent has custody so the child cannot be claimed by either parent). And yes they are that picky.

See Custodial parent and noncustodial parent  under the residency test in Pub 17

https://www.irs.gov/publications/p17#en_US_2017_publink1000170899
 
Only the Custodial parent can claim: (Child would be listed as non-dependent EIC & CC only)
-Head of Household 
-Earned Income Credit
-Child Care Credit

The non custodial parent can only claim: (Child would be listed as dependent)
-The Exemption
-The Child Tax Credit

But only if specifically specified in a pre-2009 divorce decree, separation agreement or the custodial spouse releases the exemption with a signed 8332 form - after 2009 the IRS only accepts a signed 8332 form that must be attached to the non-custodial parents tax return.

Note. If you are the non-custodial parent filing your return electronically, you must file Form 8332 with Form 8453, (U.S. Individual Income Tax Transmittal) for an IRS e-file Return. See Form 8453 and its instructions for more details.  This must be done within 3 days of your e-filed return being accepted by the IRS.

https://ttlc.intuit.com/replies/7091198

[Carl]

 First, understand that the IRS doesn't care about any court order or agreement that may exist. It holds no legal weight with the IRS. You see, the IRS is a federal agency and only a federal judge can over ride the federal laws on this. Since federal courts do not handle divorces, separations or custody issues, I can tell you with 100% certainty, that will never happen.

The IRS has their own set of rules which are based on federal law. Those rules define who is the custodial parent, and who is the non-custodial parent. Basically:

 - The custodial parent is the parent with whom the child lives for *more* than 182 nights of the tax year. (yes, nights; not days.) Those 182 nights do not have to be consecutive either. Additionally, temporary absences away from the custodial parent's home (such as to attend school, summer camp, hospital stays, etc.) count as a night spent with the custodial parent, provided the child returns to the custodial parent's home at the end of the temporary absence. In a case where the parental separation occured during the tax year, then the custodial parent is the one with whom the child lived the most nights of the tax year.

 - The non-custodial parent is the parent who does not meet the qualificiations required of the custodial parent.

The custodial parent is the parent who can claim the child as their dependent on their tax return. Period.

In cases where the non-custodial parent wants to claim the child, the custodial parent must provide the non-custodial parent with a signed IRS Form 8332 releasing their right to claim the child as a dependent, to the non-custodial parent. With that signed form the non-custodial parent can claim the child as their dependent.

So regardless of what any court order may say, the IRS rules over ride that court order if it contradicts federal law.  But that doesn't mean a lower court judge is not completely powerless.

While a lower court judge can not directly award the non-custodial parent the right to claim the child, that judge can order the custodial parent to sign IRS Form 8332, and can hold that custodial parent in contempt of court if they refuse to sign the form 8332. But under no circumstances and with no exceptions will the IRS get involved in this. Bottom line is, the non-custodial parent can not claim the child without a signed IRS Form 8332 - no matter what.