What does "Tragbarkeit" / affordability calculation mean?

As a practical rule of thumb, total housing costs — interest, amortization and maintenance — should not exceed about one third of gross income. The assumed interest rate is typically set well above the market rate to anticipate a possible rise in rates. For maintenance, institutions often use a percentage of the property value, while for amortization at least the upper financing portion (second rank) — down to roughly two‑thirds loan‑to‑value — is usually paid back within about 15 years or by retirement. These assumptions vary by lender, property and customer situation.

An example makes the logic tangible. Suppose the purchase price is CHF 1,000,000 and the mortgage is 80 percent or CHF 800,000. With an assumed interest rate of 5 percent, interest costs amount to CHF 40,000 per year. Amortizing the second rank (about CHF 130,000) over 15 years gives an annual amount of roughly CHF 8,700. For maintenance and ancillary costs a flat rate of around 1 percent of the property value is applied, i.e. CHF 10,000. Together this is about CHF 58,700 per year or just under CHF 4,900 per month. To meet the affordability criterion in this example, gross income should be roughly CHF 178,000 per year.

Which incomes and expenses are included in the calculation is also regulated. Fixed salaries count in full, variable bonuses are sometimes only partially considered. Obligations such as leasing payments, consumer loans, alimony or high childcare costs reduce the affordable share because they shrink disposable liquidity. For couples, the second partner’s income may only be partly counted depending on employment situation. At the same time, pension assets (e.g., Pillar 2 or 3a) can be used as equity or for indirect amortization, which structures the annual burden.

Affordability is not just an entry hurdle but an ongoing management tool. If interest rates, income or the market value of the property change, the financial buffer changes too. If interest rates rise significantly, the effective monthly burden increases; if income falls, the margin tightens. Conversely, a lower loan‑to‑value or higher amortization improves robustness. When comparing offers, different institutions apply different assumptions and tolerances, so careful dossier preparation and an appropriate interest and amortization strategy are crucial.

For buyers this means: solid affordability is created by sufficient equity, realistic budgeting and reserves for unforeseen events. It is sensible not only to meet the affordability test narrowly but to plan a buffer to cushion life events, renovations or interest changes. That way the financing remains affordable over decades.