I have a dependent that I claimed for 7 months but it should have been 6 months. Do I need to file an amendment?

[Critter]

To claim a dependent it has to be more than 6 months ... so if you had the child 6 months + 1 day you have to use 7 months.

[rnazario77]

It was not 6 months + 1, should I amend?

[Hal_Al]

Not yet, but probably. Let's stop talking about months and use actual dates. When did the child live with you?
You do not claim a dependent for a number of months. You a claim a dependent for all year or you don't claim him at all. The number of months you enter only determines whether you can claim him at all. The actual rule is "more than half the year": 183+ nights, 184+ in a leap year. If there is nobody else trying or wanting to claim the child; you probably don't need to amend.

[rnazario77]

I believe the actual date the child moved was around 6/19. I have a feeling someone else will try to enter a claim

[Hal_Al · Accepted solution]

There are two types of dependents, "Qualifying Children"(QC) and standard ("Qualifying Relative" in IRS parlance even though they don't have to actually be related). There is no income limit for a QC but there is an age limit, a relationship test and a residence test. Only a QC qualifies the taxpayer for the Earned Income Credit, the Child Tax Credit. 

Since the child lived with you less than half the year, he cannot be your QC dependent. It's possible that he could still be your qualifying relative, if you provided more than half his support for the whole year. But, there is a rule that says a qualifying relative dependent can not be the QC of another taxpayer. So, if the child lived with another relative for more than half the year (e.g. June 20 to Dec. 31), then you cannot claim him, even if you provided more than half his support.

So, if someone else is going to claim him, you should file an amended return, removing him.

You could "wait and see". Here's how it works, if two taxpayers claim the same child. The first one to file gets his efile accepted. The 2nd return will be rejected if e-filed. He would then need to file a return on paper. 

The IRS will process both returns and send you your refund, in the normal time. Shortly (up to a year) thereafter, you'll receive a letter from the IRS, stating that your child was claimed on another return. It will tell you that if you made a mistake to file an amended return and if you didn't make a mistake to do nothing. The other party will get the same letter you did. If one of you doesn't file an amended return, unclaiming the child, the next letter, from the IRS, will require you to provide proof. Be sure to reply in a timely manner.

Winner gets the tax benefits; loser gets to pay the IRS back with penalties and interest.  The custodial parent almost always wins. 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.  

https://www.thebalance.com/claiming-same-dependent-audit-risk-3193030