For the overwhelming majority of Americans, W2 and 1099 forms capture all of their income for the year. Yes, some small percentage (less than 20% ??) will have other adjustments to make but that’s why other countries have you verify their info.

Here in Poland you basically get the form with the numbers, add whatever else you need deducted and that's it. That if you're salaried worker, all is handled between your employer and tax office.

Here, if you are a salaried worker, your employer handles the taxes and the mandatory public insurance. When talking about wages, it is always post-tax. Good part is, you don't have to waste time or effort on your taxes, bad part (or good depending on who you are) is, nobody thinks about taxes so they don't know the absurd amount of money they pay the government every month.

If you are self-employed, all you have to do is do the regular tax bracket income tax calculation on your net income (total income - work expenses) and add the fixed mandatory health insurance cost. It is very easy and can be done through e-Devlet or your bank's mobile app/website but many people just hire an accountant because mistakes can be costlier than the minuscule cost of hiring one. Another alternative is to get all your payments through a payment processor that handles taxes for you, which is the go-to option for side hustles.

If you are an employer, you do the same as above, but for yourself and all your employees.

For all the other extra taxes (car ownership etc.) you are notified if you owe anything and the payment is again as easy as online banking or e-Devlet. I've never heard anyone complain about the process of paying taxes. The absurd amount of taxes on the other hand...