We have progressive tax (which is complicated in itself, as you pay different rates on each paycheck, so, the first N amount, you pay 0% (bit it's not called that, ofc), then up to the next N, you pay some other percentage, and of the money after that N up to the next, you pay yet another percentage).
Then we have for some reason, chosen to subsidize banks, by letting people not pay tax on the percentage of money they pay to the bank that constitutes the interest. Then there are a million other factors that might influence it..
On top of that, you're not actually only taxed for the amount of money you earn in a year, you're taxed by the amount of money you thought, last year, that you were going to earn this year.. and there's more, that I am ignorant about, because I just.. accept that it's a black box and either receive or pay the money they ask at the end of the tax year.
In fact the UK has something like that because of progressive taxation.
The idea is that a tax system should be "progressive", meaning people who earn a high income should pay a higher percentage of their income in tax, and conversely people who earn very little should pay a low, zero or even negative percentage.
Now imagine you work for two employers overlapping in time. E.g. one job in the daytimes and another in the evenings.
Your employers don't know about each other, so your total earnings before tax will not be known by either employer, but you should pay a higher percentage of tax due to your higher total income. So the state has to be involved in the calculation.
Then we have for some reason, chosen to subsidize banks, by letting people not pay tax on the percentage of money they pay to the bank that constitutes the interest. Then there are a million other factors that might influence it..
On top of that, you're not actually only taxed for the amount of money you earn in a year, you're taxed by the amount of money you thought, last year, that you were going to earn this year.. and there's more, that I am ignorant about, because I just.. accept that it's a black box and either receive or pay the money they ask at the end of the tax year.