No thread found on this forum to handle the
historical interest rates .

Interests on loans are called "Zins, Zinsen (pl.)" , which
might be rooted in the word "Zehnt" , translated "Tenth" .

A "Zentner" once had been a sack of crop weighting 50 kilograms ,
and had been a usual word in agricultue ; Doppelzentner @ 100kg .

Nowerdays the language in agriculture is also shifting ,
and some other word is used , the "Dezi-Tonne" @ 100kg .

First , a website with a chart about "Hypothekenzinsen" ,
which probably is similar to "death-gage" aka "mort-gage" :

A second website about rates in building construction :
BauZins . org

Using a chart provided by InterHyp . de :

Two German half-state background loan providers with a range of
1 to 8 % on interests , according to the worthiness of the borrower :

1.) Kreditanstalt für Wiederaufbau (KfW)

2.) Landwirtschaftliche Rentenbank : Which has a surplus for the
real front house bank already priced in to the rates ,
plus the house bank
is allowed up to 1% of the loan sum as one-time administration fee ,
at a max. of 1250 € .