Several Hypothekenvergleich sites like for example at homegate include Amortisation and Unterhalt- Nebenkosten on top of interest.
1. What is amortisation in the case of a house? Is it value degradation because of use?
2. Why unternalt- nebenkosten included? I guess they depend how much time I spend in my house and how energy efficient it is?

1. Amortisation is the principal amount that you owe back to the bank. Which means the payback from 80% amount that was mortgaged to you by the bank. The idea is that 14% of this 80% is paid in the first 15 years of mortgage. The bank setups the value based on your income, assets etc.


2. You are right on the nebenkosten part. The bank figure is just an average (I guess they put 1% by default). If it is a house, it depends on how much you spend. If it is part of a society (multiple apartments or houses which have lift, parking garage etc.), it is the collective cost. It varies from property to property .

I hope that helps
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Amortisation is paying off the debt, often you have 60% loan-to-value as interest only and the rest you have to pay off.

The others are included because they are relevant to affordability when you are thinking about buying a house.

There are tens if not hundreds of other threads on this topic...