Mortgage affordability and your real budget: two tests you need
Credit approval and household resilience answer different questions; calculate both before bidding.
The lender’s test is a starting point
A financing calculator is most useful when you understand what it is testing. A lender considers accepted income, equity, valuation and its own sustainable lending criteria. Your household budget asks a different question: what money remains after housing, children, transport, insurance and saving? Passing the lender’s test does not establish that every lifestyle commitment is affordable. Conversely, current low interest payments do not necessarily demonstrate that the loan will pass a stressed assessment at renewal or retirement.
Separate assumptions from quotations
Use an explicitly labelled stress interest rate for resilience, then a separate quoted contractual rate for current cash flow. Add amortisation, recurring charges and maintenance assumptions to both as appropriate. Do not present a common planning convention as a universal legal threshold or a guaranteed credit decision. Ask the proposed lender which income it accepts, which valuation it uses and how irregular pay is treated. Its written answer matters more than a green indicator on an online calculator.
Hypothetical sensitivity
For an unchanged CHF 600,000 loan, an additional annual interest percentage point costs CHF 6,000, or CHF 500 monthly, before amortisation and maintenance. A household with CHF 300 free monthly cash flow cannot absorb that change without adjustment. These invented figures are not offered rates or an underwriting result. Repeat the exercise on your debt and show the surplus after all essential spending. The arithmetic makes rate exposure tangible without trying to forecast future central-bank decisions.
Include the costs that listings omit
A property listing rarely describes your full cost of ownership. Obtain actual charges where available, inspect likely repairs and budget for insurance, utilities and transaction expenses. A percentage maintenance assumption is a placeholder; an ageing roof or heating system deserves a separate estimate. Keep an emergency reserve outside the purchase funds. The most attractive advertised price may be accompanied by work that arrives shortly after completion, when the household has already committed much of its cash.
Test changes in income
Model a parental-leave period, reduced hours, job loss and retirement using realistic income assumptions. Check insured benefits separately rather than treating protection as an automatic replacement of salary. If two incomes are required, examine how long the household could continue on one. A self-employed or bonus-heavy income profile should be reviewed with the lender before a binding commitment. Include the timing of annual taxes and other large payments so an apparently positive average does not hide a cash shortage.
A useful buying decision
Keep a lender assessment beside a household cash-flow forecast and a short list of unresolved property costs. If one test fails, change the price range, equity plan or timing before stretching assumptions. FINMA’s mortgage-risk guidance provides context for cautious lending; it does not approve individual borrowing. The decision should leave room for ordinary disruption and long-term saving. A sustainable purchase is one you can keep funding after the excitement of completion and under conditions less favourable than the first quotation.
Sources and further reading
Original Clearwise analysis. External reporting provides context; rules and contract terms must be verified with the competent authority or provider. Some press articles may require a subscription.
Apply this to your situation
Compare your actual documents and clarify what matters before making a commitment.
Request a free consultationGeneral guidance, not a binding quote or personalised legal, tax or investment advice. Examples are hypothetical and results are not guaranteed.
