How much interest rate buffer do you need for a SARON mortgage?

The 3-column buffer rule

For secure SARON financing, you should calculate a real interest rate buffer of at least 2.0 to 2.5 percent above the current interest rate. This consists of three elements: A liquid reserve for short-term interest peaks, a maximum budget burden of 30 percent of income with a simulated interest rate of 4 percent, and the contractual option to be able to switch to a fixed-rate mortgage at any time without charges.

Imputed interest rate vs. lived reality

Anyone applying for a mortgage in Switzerland will inevitably come across the affordability calculation. Banks calculate with a theoretical interest rate of usually 5 percent, plus service charges and amortization. This strict requirement is intended to ensure that the entire financial system survives even severe economic crises. But be careful: This value is just a shield for the bank, not a tailor-made financial plan for your private household. A portable model therefore requires looking at your own real budget books instead of the standardized tables in the credit department.

If the real SARON rate rises from 1.0 to 3.5 percent, for example, the bank won't collapse, but your monthly transfer for the mortgage increases massively. The imputed check does not protect you from real liquidity outflows in everyday life. It simply means that you won't go bankrupt in theory. However, it does not take into account your individual standard of living, planned investments or changes in income due to future part-time work. Anyone who calculates the interest buffer on the basis of the bank bill alone weighs themselves in a dangerous false security.

Calculating the stress test: How to determine your Swiss franc requirement

To determine your actual buffer requirement, you must translate the abstract percentages into hard Swiss francs. The leverage effect of large loan amounts is underestimated by many homeowners. Let's take a typical mortgage amount of 1,000,000 francs as an illustrative settlement basis.

Assuming a SARON total interest rate (including banking margin) of 1.5 percent, interest costs amount to 15,000 francs per year, which corresponds to a monthly charge of 1,250 francs. If the SNB raises the key interest rate in the fight against inflation so that its total interest rate rises to 3.5 percent, the annual burden rises to 35,000 francs. That means a monthly charge of 2,917 francs.

The difference is therefore 1,667 francs — every month. Your real interest rate buffer must be able to close exactly this gap without you having to immediately go to the iron emergency reserves. Should interest rates remain high over a longer period of time, this amount quickly adds up to tens of thousands of francs missing elsewhere in the household budget. A healthy buffer is available when this additional burden is covered by current cash flow or when there is a reserve of at least two annual differences in a savings account.

Monetary policy is not a one-way street

As a money market interest rate, SARON reacts directly to monetary policy decisions in Bern. The central bank uses the key interest rate to manage domestic inflation and stabilize the Swiss currency. For homeowners, this means that periods of low interest rates can be ended at any time due to macroeconomic shocks. If global inflation rises, rapid interest rate increases are the logical consequence. In an export-oriented economy such as Switzerland in particular, global supply chain problems or geopolitical tensions can radically change the SNB's monetary policy orientation.

In practice, phases of interest rate rises are rarely linear or smooth; the markets often drastically adjust their expectations upwards within a few months. Anyone who holds a SARON mortgage should not be dazzled by the current cosiness of the market. The required interest rate buffer is not a static variable, but must be assessed countercyclically. In periods of low interest rates, the buffer should mentally be set larger than in times when interest rates are already close to the historical average.

Tactical protection measures for your budget

Anyone who opts for the money market should take accompanying measures to structurally limit the risk. There are proven strategies that can be used to artificially increase the financial buffer:

• The calculated long-term savings: Pay yourself a fixed rate of, for example, 3.5 percent on a permanent basis. You transfer the difference to the actually lower SARON interest rate to a separate savings account. If interest rates rise, pay the additional costs out of this pot. Stay low, build up wealth.
• Strategic run-time mix: Divide the total amount of the mortgage. A portion of SARON absorbs interest rate cuts, while parallel fixed-rate mortgages cap the risk upwards.
• Contractual exchange guarantee: The option to quickly convert a SARON mortgage into a fixed-rate mortgage with the same institution reduces the cash buffer required, as you can pull the rip cord in an emergency.

The forgotten component: customer margin and credit rating

A common mistake in budget planning is confusing the pure SARON rate with the ultimate retail interest rate. The SARON only forms the basis of the product. Each financial institution adds an individual customer margin, which is based on your creditworthiness, the equity contributed and negotiation skills. In Switzerland, this margin is usually between 0.5 and 1.2 percent.

You must regard the margin as a fixed, invariable basis. If SARON is zero, you still pay your margin. If SARON rises to 2 percent and your margin is 1 percent, the effective interest rate is already 3 percent. The interest rate buffer must always be based on this cumulative final interest rate. Also check whether the bank has the right to adjust the margin if your financial situation worsens. Make sure that the framework period of the SARON contract does not force you unprepared into a phase in which renegotiations must take place on significantly worse terms.

Conclusion: Liquidity secures the dream home

The question of the optimal interest rate buffer cannot be answered with a fixed percentage, but requires honest and detailed accounting of one's own finances. Theoretical survival on bank paper is not enough in everyday life if every rise in interest rates on the market triggers existential concerns.

In summary, a real interest rate buffer of at least 2.0 to 2.5 percent above the current market level is the golden rule for relaxed home management. Anyone who consistently saves the difference between low interest rate and potential crisis interest rate makes optimal use of the benefits of the money market without taking risks. Combined with clean monitoring of central bank policy and the flexibility to be able to switch to a fixed-rate mortgage in an emergency, the SARON model becomes a calculable financing strategy. Plan ahead to keep your Swiss residential foundation stable in the long term.

Risk analysis glossary

• affordability calculation: Banks' standard audit procedure, which checks whether the running costs of a property (calculated at 5% imputed interest) do not exceed one third of gross income in the long term.
• Customer margin: The percentage premium that the Swiss bank calculates on the base money market interest rate (SARON) to cover its own administrative and risk costs and to generate its profit.
• Money market mortgage: A credit product whose interest rate is not fixed for years, but is based on the official rates of the money market at short intervals (usually daily or quarterly).