Only if you let him.The custodial parent has first priority on claiming the children on her taxes; regardless of the amount of support provided by the non-custodial parent. The IRS goes by physical custody, not legal custody. The non-custodial parent can only claim the child as a dependent if the custodial parent gives permission (on form 8332) or if it's spelled out in a pre 2009 divorce decree. Even if a divorce decree, dated after 2008, gives the non-custodial parent the right to claim the child, he must still get form 8332 from the custodial parent. A properly worded decree should require her to provide that form. https://www.irs.gov/pub/irs-pdf/f8332.pdf
Chances are, you are not getting full benefits from all 5 kids, and should probably let him claim some. But the only way to be sure is to do tests returns with the various combinations. This tool may help https://turbotax.intuit.com/tax-tools/calculators/taxcaster/?s=1.
There is a way to split the tax benefits.
This may be helpful in your negotiations with the ex:
There is a
special rule in the case of divorced & separated (including never married) parents.
When the non-custodial parent is claiming the child as a dependent/exemption/child
tax credit; the custodial parent is still allowed to claim the same child for
Earned Income Credit, Head of Household filing status, and day care credit.
This "splitting of the child" is not available to parents who lived
together at any time during the last 6 months of the year; then only one of you
can claim the child for any tax reasons. The tax benefits may not be split in
any other manner.
Note in particular
that the non-custodial parent can never claim the Earned Income Credit, Head of
Household filing status or the day care credit, based on that child, even when the custodial parent has released
the exemption to him.
So, it's good idea to let the other parent know that you
will be claiming those items, as many first time divorced parents are not aware
of this rule and may try to claim those items, which will cause the IRS to send
out letters.
Ref: http://www.irs.gov/publications/p17/ch03.html#en_US_2014_publink1000170897
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separated parents (or parents who live apart)"
