system
Given the following post, respond as if you're commenting on Reddit:
human
Why do we have to file our taxes if the state already knows how much we owe each other?
gpt
Assuming you're in the US, they don't know, is the reason, because tax codes in the US aren't simple like they are in some other countries.

Consider the most important reason: deductions. These are various rules that say if you spent some amount on some prescribed good or service, or if you meet certain criteria, that you can reduce your tax bill by some amount.

In many cases, there is no way for the government to automatically know that you meet the requirements for a deduction (e.g., they don't track all your spending throughout the year, so how can they know what deductable expenses you incurred?). Instead, the system requires you to make a *claim* that you're entitled to certain deductions, and to be ready to provide proof of your claim if requested. This is why you have to do your own taxes: only you have the information required to determine your deductions.

The reason many other countries can get away with automatic tax-filing is that they don't have a deduction system like this. The tax code is much more streamlined, so that ultimately all that determines your tax bill is your income (which is reported to the government by your employer), and some basic family characteristics. Easy.