Congratulations! The more allowances you put on your W4 the less taxes are taken out. If you have been getting a big refund you can change it to 4, but if you have been owing taxes or get a very small refund you may want to keep it to 3. If you are not exempt you would choose no exempt. See the following for more information regarding a W4
Withholding Exemptions - Personal Exemptions - Form W-4
https://www.irs.gov/Individuals/International-Taxpayers/Withholding-Exemptions---Personal-Exemptions...
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Note: When you claim your son on your 2015 tax return, when it asks how long did he live with you, select the Whole Year. A child who was born during the year
(even if on the last day) is treated as having lived with you all year