Interest swap – deductible? not deductible?

The taxpayer pays for cover on a mortgage interest rate swap.

The tax authorities consider that these are not deductible mortgage interest.

Federal judges describe the financial instrument: «Interest rate exchanges, also known as interest rate swaps (or simply swaps), are transactions in which the contracting parties exchange interest payments in a given currency. They agree upon the dates of exchange for the interest payments, the level of the respective interest rates, the duration of the agreement, and the notional amount (underlying) upon which the interest payment is based. The notional amounts are not exchanged, but merely serve as a calculation basis for the interest.".
Thus, an interest rate swap is a transaction in which interest is not paid to the counterparty in return for the provision or use of capital, but solely in return for the interest that it has committed to pay. As the name «swap» indicates, it is quite simply an exchange transaction, i.e. the exchange of (differing) interest amounts calculated by reference to the underlying asset. As a rule, it is not the «interest payments» themselves that are exchanged, but the reciprocal payment obligations that are offset. Only the ’interest surplus« is paid – that is, the amount by which one party's payment obligation exceeds the counterparty's reciprocal obligation (surplus offsetting or »netting«).
Interest rate swaps are derivative financial instruments whose value, as stated, depends on that of another product. These are operations that are not traded on a stock exchange, but directly between the operator concerned (generally a bank or an insurance company) and the end consumer.» (point 7.1.)

The federal judges then carry out a concrete analysis of the case regarding the link in casu between the Swap and the mortgage interest. (cons. 7.2.2.)

They conclude that «there is no sufficient link between the payment related to interest rate swaps and the capital debt in the form of LIBOR loans. The payment in question cannot therefore be treated for tax purposes as passive interest.» (cons. 7.2.3.)

The judgment is in German. It is a Zurich case.

Federal Tribunal, judgment 9C_261/2025, of 11 March 2026