In the consultation it is said that your interest rate follows market conditions. For a concrete German consumer loan agreement with an index‑linked variable nominal interest rate this statement alone is too imprecise. You should be able to trace the quantity used and the method by which the interest actually charged is calculated.
§ 492 Absatz 7 BGB requires for a nominal interest rate variable according to an index or reference rate an objective, clearly determined and for both parties available and verifiable index or reference rate. [BGB492-7] Whether a particular clause is effective and what consequences a problem would have is not decided by this article.
Read the name in full
Copy down the exact contractual designation of the reference quantity and note the place where it appears. Ask where the value relevant under the contract can be checked. Similar names or different time references are not equated simply because the same familiar market term appears somewhere.
Supplement the reading and adjustment dates relevant under the contract as well as any expressly provided margin and further calculation steps. If these details are unclear, ask for an explanation based on the actual contractual text. an internet value from today does not automatically correspond to the last interest determination.
A fictitious example clause
For a simple comprehension test we assume a clearly defined reference quantity of 2,1 per cent and an expressly agreed margin of 1,2 percentage points. Without further clause elements the sum would be 3,3 per cent. None of these values is a current market quotation or a real condition.
In the actual contract additional provisions may be relevant. This simplified calculation step must therefore not be transferred to it without verification. A contractual rounding, limit or a different reference date must be explained instead of being replaced by an assumption of your own.
Understand the interest rate first, then the instalment
A declared interest rate does not yet answer all questions about the new monthly instalment. Among other things the actual outstanding amount and the repayment history of the specific contract are required. Have the responsible party show the connection between altered interest charging and the payment schedule.
Record the answer together with the relevant date. If your own calculation differs, specify exactly the reference value used and the step affected. This turns “The instalment seems too high” into a verifiable question.
Seek appropriate advice if a clause question is open
An unclear formulation is a reason for further explanation and, if necessary, specialist examination. This article does not recommend ceasing payments on your own initiative. The aim is a comprehensible contractual basis and a clearly described open question before you derive far‑reaching consequences from a single difference.