Buy an apartment on credit and rent it out

If it goes wrong, your rental income could push you into a higher tax bracket. Then you pay a higher tax rate on your entire income.

That does not correspond to reality.

tax-wise it looks like this:

gross rental income
- loan interest
- service charges
- depreciation
- maintenance expenses
- property manager fees/other expenses
= surplus
x marginal tax rate
= additional income tax

Many forget that the reserves in the service charges only cover costs for building repairs. Everything that needs to be done inside the apartment must be paid out of pocket. As Nordanney already wrote, if the reserves are too low, an additional special assessment may also be imposed.

Besides, I believe I heard that with a rental property you cannot get 110% financing. You must at least contribute the incidental costs (real estate transfer tax, broker, notary) as equity.

If the substance is okay, the object is manageable, and the target group for renting is available, I would do it. However, only if everything else is financially settled and a vacancy of a few months is manageable, and the nerve for possible disputes with tenants or co-owners is present.

You forget in your calculations the depreciation on the substance, which is also deductible as advertising costs and reduces the tax burden.

Assume 2 percent on the building substance.

Usually, 20-35 percent is considered as acquisition cost for land (not depreciable) and the rest (65-80 percent) as the depreciation basis.

If the building was completed before 01.01.1925!, the depreciation is 2.5 percent p.a..

What else comes to mind. Especially small apartments have, at first glance, a better return due to the higher rent prices per square meter.

However, certain repairs/modernization costs are just as expensive as in a large apartment (e.g., toilet/shower). The size of the apartment is also probably irrelevant to property managers, who are likely to charge a uniform management fee per apartment.

Before I deal with capital investments, if I were you, I would address the topic of owner-occupied property. If you have a fully paid-off apartment/house, willing to take risks and have a few euros to spare, you can become a landlord.