An offer divides the mortgage into a fixed‑rate and a variable part. The label mixed does not yet explain how much additional payment the household would have to bear in the event of a change. What matters is which amounts come due at which points in time. This Austrian case for decision does not choose a suitable split for you, but makes the combined burden verifiable.
Show each sub‑financing as its own trajectory
Record for each part the amount, current instalment, interest phase, outstanding balance and intended end. The FMA distinguishes fixed interest rates for the agreed period from variable interest rates. [FMA-ZINS] The linked issue is partly set in a historical low‑interest context; its example terms at that time are not used here.
Ask for the actual offer how changes in the variable part will take effect and which rule is envisaged after the end of the fixed section. A description such as half fixed does not prove that the total instalment will change by at most half, nor that both parts will be repaid at the same pace.
The household has only one margin
In the fictional starting case the instalment for the fixed part is 700 Euro and that for the variable part 400 Euro. Together that is 1.100 Euro. For an assumed stress scenario a separately assumed sub‑plan states 580 Euro instead of the 400 Euro. The total instalment would then be 1.280 Euro; the additional need is 180 Euro.
This is not a bank instalment calculated from market interest rates. The two instalments are explicitly stipulated case assumptions. The household adds the 180 Euro alongside its other monthly expenses. A percentage share of the loan does not answer this euro question.
Do not hide the later date
Create a second line for the end of the fixed phase. What debt would then remain in each part? Which instalments would have to be paid simultaneously under the respectively disclosed assumptions? Have this later trajectory calculated based on the contract. The amount that has been fixed so far is not silently continued until the final end of the loan.
Also check organisationally whether different due dates, evidence requirements or possibilities for change exist for both parts. A possible special repayment is taken into account only for the part actually affected, not doubled across the board.
Base the decision on a comprehensible sentence
Formulate your result concretely: Which total burden is fixed today, which can change and which later section is open? If this answer is only possible with vague buzzwords, an explanation is still missing. A split financing can be the subject of advice; its name does not replace a household budget.