Yes ... it is applied towards federal income tax of any kind. It cannot help you with other taxes like SE or penalties. 

Is There A maximum that can be applied?

Yes ... it is limited to the credit or the tax which ever is less ... also the credit may be limited by other non refundable credits which must be used first ... any unused credit will carry forward.

Review the form 1040 & 8839 to see how they work together ...

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