When one speaks of deducting the tax, does that only reduce the profit and thus the tax or directly the tax on the amount deducted?

Example I would have to pay 10,000 euro in taxes (result of income - expenses times personal tax rate).

Suppose I want to buy a laptop for 2000 euro for my studies. If these 2000 euro are now deducted directly from the 10,000 euro euro, which means I only have to pay 8,000 euro, or are the 2000 euro added to the expenses, which means that I have made less profit that has to be taxed, i.e. That would only be marginally 10,000 euro lower.

Typically, tax deductible investments reduce the taxable profit, not the tax amount.

The 2000, - costs lower your profit. So you pay taxes on a lower profit.

Your tax liability does not decrease by the 2000, -, but only by the taxes that you would otherwise pay on the 2000. With a tax rate of 25%, for example, your taxes will decrease by 25% from 2000, - i.e. 500, - with the purchase.

According to the basic table, 10k taxes are required for a taxable income of 42K. For that you need a net income of around 55k. How do you do that as a student? Hardly with a full-time job on an income tax card

Spending reduces your profit and thus your taxable income. If this is certain, the https://www.steuerschroeder.de/Steuerrechner/Einkommensteuer-Tabelle.html#Grundtabelle will be looked up and a tax with the corresponding percentage tax rate will be issued. The lower the income, the lower the tax rate. That means: Everything that you can claim affects the entire tax liability.

According to the objective net principle, advertising costs and business expenses reduce the taxable income, so that a lower taxable income (zvE) comes out.

Only tax reductions are deducted directly from the collectively agreed income tax, e.g. B. Tax reductions for household services.

So everything that is directly related to your taxable income as an expense (advertising costs and business expenses) only reduces the income and thus not directly the collectively agreed income tax (only via a lower ZvE)