L-1 and L-2 Visa holders need to determine if they meet the substantial presence test. Tax Tips for Resident and Non-Resident Aliens details this test in the section "Counting 183 days". If your wife is arriving on December 30th of this year, it's unlikely that she'll fulfill the requirements of this test. You can determine your best filing status by preparing your return with two different filing statuses: married filing jointly and married filing separately. Unfortunately, a spouse can not be claimed as a dependent. If your withholding is being calculated as a single individual, you are having more withheld than if you changed to a married individual. I wouldn't suggest changing your withholding amount until after determining what you may owe in tax for the current year.
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