Understanding SARON: How the Swiss benchmark rate works

Following the global phase-out of LIBOR, the Swiss financial market transitioned to SARON (Swiss Average Rate Overnight) as the reference rate for money market mortgages. Administered by SIX Swiss Exchange, SARON is a transparent, transaction-based interest rate based on real overnight repo market transactions between financial institutions in Switzerland.

Unlike fixed-rate mortgages where your interest rate is locked for 5, 10, or 15 years, a SARON mortgage is a money market mortgage whose interest rate fluctuates dynamically in line with central bank policy. When the Swiss National Bank (SNB) adjusts its key policy rate, SARON reacts almost instantaneously.

Your effective SARON mortgage rate is calculated as: Effective Interest Rate = Compounded SARON + Bank Margin. The bank margin (typically between 0.50% and 0.95%) is fixed for the duration of the contract (usually 3 to 5 years), while the compounded SARON component is calculated retroactively over a 1-month or 3-month observation period.

Fixed-rate vs. SARON mortgages: Cost, risk, and predictability

Choosing between a fixed-rate mortgage and a SARON money market mortgage is the central strategic decision when financing Swiss real estate:

1) Fixed-Rate Mortgages (Festhypothek): Provide 100% budget certainty. You lock in a fixed interest rate (e.g., 1.80%) for 5 to 15 years. You are completely protected if inflation or SNB rates rise. However, if interest rates drop, you cannot benefit from lower rates, and breaking a fixed-rate contract early incurs severe penalty fees (Vorfälligkeitsentschädigung).

2) SARON Mortgages (SARON-Hypothek): Offer maximum flexibility and historically lower average interest rates over long observation periods. If interest rates fall or remain low, SARON borrowers enjoy lower monthly payments. However, if the SNB raises rates to combat inflation, your monthly interest costs will rise immediately at the next compounding period.

3) Conversion rights: Most Swiss banks grant SARON mortgage holders the contractual right to convert their SARON loan into a fixed-rate mortgage at the end of any compounding quarter without early cancellation penalties.

Bank margins, floor clauses, and compounding periods

When comparing SARON mortgage offers from Swiss banks (such as UBS, Raiffeisen, Migros Bank, or cantonal banks), borrowers must scrutinize three critical contractual elements:

1) Bank Margin (Marge): The bank's profit margin added on top of SARON. High-creditworthiness borrowers can negotiate margins as low as 0.45% to 0.60%, whereas standard quotes average 0.75% to 0.90%. A difference of 0.20% on a CHF 800,000 mortgage equals CHF 1,600 per year in interest savings.

2) Floor Clauses (Zinsuntergrenze): In negative or zero interest rate environments, banks impose a floor clause stating that if SARON falls below 0.00%, the base SARON is set to 0.00%. Consequently, your minimum interest rate equals the bank margin.

3) Compounding Method: Most Swiss banks use the Compounded Swiss Average Rate Overnight over a 3-month period ('SARON Compound'). At the end of the 3-month period, the interest rate is calculated based on daily rates during that quarter and billed.

Hedging strategies: Tranche splitting and rate risk management

To balance predictability with cost optimization, Swiss financial advisors frequently recommend mortgage tranche splitting.

For example, on a total mortgage of CHF 1,000,000, a buyer might divide the loan into two tranches: CHF 500,000 in a 10-year fixed-rate mortgage to secure a baseline budget, and CHF 500,000 in a 3-year SARON mortgage to benefit from lower short-term money market rates.

Before deciding on a financing structure, evaluate your overall property ownership math using our guide on buying vs renting in Switzerland, review mortgage qualification criteria in our Swiss mortgage guide for expats, and stay informed about the abolition of imputed rental value (Eigenmietwert) which impacts future mortgage tax deductions.