Do you remember how many withholding allowances you claimed on the last W-4 you filled out? That's the form you have to complete when you begin a new job, so your company's payroll knows how much federal income tax to withhold from your pay.
As New Tax Laws Take Effect, Check Your Withholding Amount
The IRS advises that you complete a new W-4 every year, and also when your "personal or financial situation changes"--a big raise, marriage, have a child, etc. If you remember to do this regularly, congratulations; you're a step ahead of most people, I would suspect.
If you haven't revisited this form for a few years, now is a good time. Read full article