If you've ever filled out a 1040, you know the U.S. tax system and the agency that keeps it going are complex and mystifying entities. Get the lowdown on this essential piece of the U.S. government.

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The Tax Process

While most Americans only think about taxes when April approaches, the tax collection process actually runs all year long.

The process begins when you start a new job. You and your employer agree on your compensation — an hourly wage or an annual salary — which adds up to your gross or "before tax" income. The next thing you do is fill out a W-4 form. The W-4 form is like a miniature income tax survey. It determines if you are single or married, if you have children or other dependents, if your spouse works and if you have childcare expenses. These are called your personal allowances. The number of allowances listed on the W-4 form determines how much income tax your employer will withhold from each paycheck.

Why does your company do this? Because employers are required by law to withhold income tax from all employee paychecks and deposit the money in a Federal Reserve Bank. This is how the federal government maintains a steady stream of income while also drawing interest on your tax dollars. Instead of paying taxes once a year in April, you really pay them all year long.

The W-4 form is important because it ensures that you aren't paying either too much or too little in federal income tax during the year. Some people love to get a big refund check when they file their tax return in April. But what that really means is that they paid too much income tax during the year. They could have put that money in the bank, invested it, or bought something useful with it rather than letting the IRS borrow it. By adjusting the number of allowances on the W-4 form, you can decrease or increase the amount withheld from each check. That way, there are no big checks or big bills in April. Check your W-4 annually to make sure the information is up to date.