This article reflects the state of our research and is not legal or tax advice. What applies to your property depends on the zone, the municipality, the house rules and your contract; only the competent authority gives binding information.
Key facts
- Income from short-term letting is usually not treated like rent when affordability is assessed.
- Banks calculate with imputed interest rates well above the current one, plus amortisation and incidental costs.
- The overlooked risk is in the contract: mortgage agreements regularly contain provisions on how the property is used.
- Switching from own use to commercial accommodation is a change of use — ask your bank in writing before you switch.
The assumption that goes wrong
The calculation many people make runs like this: the flat brings in more with short-term letting than with a long-term tenancy, so it carries a larger mortgage. Both halves are correct on their own, but not together.
Banks calculate affordability using notional rates — usually an interest rate well above the current one, plus amortisation and running costs. For let properties the rental income is taken into account. Income from short-term letting, however, fluctuates, is seasonal and is not secured by contract. It is therefore frequently not counted at all, or only with a discount.
That does not mean short-term letting is not worthwhile. It means it does not expand the financing. Anyone justifying a larger mortgage by the larger income is arguing past the affordability calculation.
Your figures, not our examples
The calculator takes the number of rooms, the neighbourhood and the fit-out and shows you a range — with the arithmetic beside it, not as a single figure you have to take on trust.
Estimate the returnThe risk that is in the contract
The point considered less often: mortgage contracts and the underlying terms regularly contain provisions on the use of the property. A switch from owner-occupied residential space to commercial accommodation can be a change of use subject to notification.
The consequences vary and depend on the contract: a different loan-to-value limit, a different interest rate, or a requirement for additional security. Owner-occupied residential property is typically financed on better terms than investment property.
The practical advice is unspectacular and rarely followed: speak to the bank before the switch, not after. A conversation you seek out yourself goes differently from one the bank seeks out after learning about the use.
And the tax side
With owner-occupied residential property the imputed rental value (Eigenmietwert) is taxable. If the flat is let in part or in whole, the treatment shifts: the rental income is taxable income, and the imputed rental value has to be adjusted accordingly.
How that looks in an individual case depends on the split between own use and letting and is handled differently from canton to canton. This is the classic case where an hour with a tax adviser is cheaper than a year of uncertainty.
Frequently asked questions
That depends on the contract, and the question belongs before the switch, not after. Mortgage contracts regularly contain provisions on the use of the property; a switch from owner-occupied residential space to commercial accommodation can be a change of use subject to notification. Possible consequences: a different loan-to-value limit, a different interest rate, additional security — owner-occupied residential property is typically financed on better terms than investment property. A conversation you seek out yourself goes better than one the bank seeks out.
Usually not in the way it counts rent. Banks calculate affordability with notional rates and look to secured, predictable income. Income from short-term letting fluctuates, is seasonal and is not secured by contract; it is therefore frequently not taken into account at all, or only with a discount. The practical consequence: short-term letting increases your income but not your borrowing capacity. Anyone justifying a larger mortgage by the larger income is arguing past the affordability calculation.
It shifts. With owner-occupied residential property the imputed rental value (Eigenmietwert) is taxable; if the flat is let in part or in whole, the rental income is taxable income and the imputed rental value has to be adjusted accordingly. How the split between own use and letting is treated in practice differs from canton to canton. This is not a question that can be settled with a calculator on the internet — an hour with a tax adviser is cheaper here than a year of uncertainty.
And for your property?
Sources
State of our research: 16 July 2026. Official rules change — check the current position with the competent authority.
