My niece lives with her aunt 6 months out of the year and uncle myself and her aunt in are home 6 monthe out of the year we have joint custody can we both claim her?

[Opus 17]

No.  Only one person can claim a child as a dependent.  It will be the aunt or uncle where the child lives more than half the nights of the year.  In most years (with an odd number of days), it's not possible for custody to be exactly equal.  The child will live in one home for 183 or more nights, and the home for 182 or less nights.

In the rare event the child lives an exactly equal number of nights with each aunt or uncle, then the adult with the higher adjusted gross income can claim the child.

[NCperson]

Not sure I am following all the aunts and uncles 

whomever the child lives with MORE THAN HALF THE YEAR can claim her.  That can only be one taxpayer.

So to state she lives with one set of taxpayers for 6 months and another set of taxpayers for the other 6 months probably isn't factually correct.  If you checked it off on the calendar (and you'll need to do that if it is that close to 6 months for each), who does your neice spend more nights with during the year?  

You may need to provide this forum with more facts. 

Legally, who are her guardians? how old is she? who is paying more than 50% of her support? 

if I followed correctly ]

1) neice lives with her aunt for 6 months of the year

2) neice lives with you, her uncle (your husband???) and that same aunt for the other six months of the year. 

[Opus 17]

@NCperson 

@oconnor 

The legally named guardian doesn't matter in this case.  A child can be claimed as a dependent by an aunt or uncle (including someone who is an aunt or uncle by marriage) without a custody order or guardianship, as long as the child lives with their aunt or uncle for more than half the nights of the year.  An aunt or uncle has the same rights to claim a child as a dependent as a parent.

But you do need to count nights.