I understand, no worries. So the employer is in charge of withholding and paying in the social security and Medicare part. That is a requirement and is employer's responsibility. When it comes to federal withholding, it is up to you to let your employer know, by using the form w-4, how much federal tax you want withheld from your paycheck. This is your responsibility. If you do not withhold enough, you will owe, if you take out too much, you will get this money back as a refund when you file your taxes.
If you fail to provide a w-4 to your employer, they are required to withhold your federal taxes at a single tax rate, which is the highest.
Some people, like myself 🙂 like to withhold a little extra, and that way I get a higher refund at the time of filing my tax return. Some people like to hold on to their money, and pay to the IRS when they file their return. The down side of this is that there may be penalty involved with this. Either way, you still end up paying the same federal tax amount based on your filing status, income and dependent's situation. w-4 form is just a tool to help you plan ahead.
