Banks apply two rules. First, equity: at least 20% of the price. Second, affordability: the theoretical costs of the property (interest calculated at a rate of around 5%, amortisation and maintenance) must not exceed one third of your gross income. In practice, a household can aim for a purchase price of around five times its gross annual income: with an income of CHF 150'000, a property of around CHF 800'000. The precise calculation is done with the bank or a financing specialist, before viewings, not after.