Yes you must complete your new W4 because the tax laws changed and new W4 calculates withholdings based on new tax law.
For completing your new W4 fill up steps 1and 5, complete steps 2, 3 and 4 only if it applies to your situation. Once you complete the form, give it to your employer. Then, keep a close eye on your next few paychecks to see how the changes impacted your federal income tax withholding
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