> The IRS already knows everything about your income that you would be telling them anyway. Not even close. For example they don't know how much you paid in s

> The IRS already knows everything about your income that you would be telling them anyway. Not even close. For example they don't know how much you paid in state taxes, and which portions of that are also considered okay for fed taxes. Eg in California a portion of your annual vehicle registration fee can be taken against state taxes. Do the feds also allow that? They don't know what you consider business expenses. They don't know how much of your house you used for business purposes. They don't know where you resided during the year and the tax treatment of the various places you did live. They don't know about your moving expenses. They don't know about income you received in cash. They don't know about your Amazon purchases. They don't know about your medical expenses. They don't know about your losses. They don't know about your foreign income or assets. They don't know about dependents, or how they have changed. Or your marriage, or divorce. Or how you want your married taxes to be treated (there are at least two different ways). That is just scratching the surface of the tax relevant things - there are a huge amount more. As an individual you couldn't get your tax return 100% correct, and the government certainly can't. Edit: various institutions and employers are required to file information with the IRS. However this is big picture information - for example how much interest you were paid on your bank account, or what the employer paid you. They do not get individual transaction information, cash withdrawals or similar details.