It’s because they **don’t** know exactly how much you owe in taxes.
Taxes in America are also complicated. There are many ways to pay less taxes, but it depends on your situation. Since the IRS doesn’t know how you live, they don’t know how much you owe.
You can pay less tax if you have children. You can pay less tax if you have a home office for running a small business. You might need to pay more tax if you’ve earned money that nobody told the IRS about.
These are things that you tell the IRS on a document once a year. That document is a tax return.
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