Whether passive interest on a Swiss immovable property owned by non-residents must be allocated proportionally among domestic and foreign assets for federal direct tax.
Yes. For limited tax liability based on Swiss real estate, debts and passive interest are allocated proportionally according to the location of assets; foreign excess interest is not deducted if it would reduce Swiss-source income below the Swiss taxable base and minimum rate.
Art. 6 and 7 LIFD require proportional allocation by asset location. The mortgage debt is not so closely linked to the Swiss property that it must be allocated exclusively to it. Foreign excess interest cannot be used to reduce the Swiss tax base below Swiss-source income.