Rent reduction: your rights and the net calculation (landlord)
A tenant sends you a request to reduce the rent, usually after a drop in the reference mortgage interest rate. You are not required to reduce it spontaneously, but as soon as a written request arrives, a 30-day deadline begins to run (art. 270a para. 2 CO) and the relative method governs the calculation. The reduction owed is not the gross reduction claimed by the tenant: it is a net reduction, obtained after offsetting the increases not yet passed on, and sometimes nil. This guide sets out what you need to check, calculate and answer.
Updated 09.2026
The procedure in four steps
- 1Check the grounds for the request
The most common ground is a drop in the reference mortgage interest rate since the last valid setting of the rent, but art. 270a para. 1 CO covers any significant change in the calculation bases that would give you an excessive return (a fall in costs, a net return that has become excessive). You therefore cannot dismiss a request solely because it does not invoke the rate: examine it on the merits. For the rate ground, compare the reference rate applied at the last setting (initial rent, last uncontested increase or reduction) with the current rate published by the Federal Housing Office. If the rent was already set at the current rate, no reduction is owed on this ground. Also check the type of lease: an indexed lease (art. 269b CO) or a stepped lease (art. 269c CO) does not give rise to a reduction on this basis.
- 2Calculate the admissible net reduction
The gross reduction is read off the scale in art. 13 OBLF: about 3% of rent for each 0.25% step when the reference rate is below 5%. The method is two-sided: against this reduction you set the increase factors that have arisen since the last setting and have not yet been passed on, namely 40% of the rise in the CPI (art. 16 OBLF), the increases in maintenance and operating costs actually borne (art. 269a let. b CO) and the increase reservations validly notified. Each factor is expressed as a percentage of the net rent; apply a single method of combination throughout the calculation (imoz adds the percentages, as the usual cantonal forms do). Each factor set off must also be proven, a statement or invoice for the costs, a dated index for the CPI, a notice of reservation for the reservations; failing which it is disregarded in conciliation and the net reduction owed rises accordingly. The resulting figure is the net reduction, often lower than the gross reduction, sometimes nil; imoz calculates it item by item.
- 3Reply in writing within 30 days
Date the receipt and reply in writing within 30 days (art. 270a para. 2 CO), with reasons and figures. Three replies are possible: accept the net reduction owed, grant it in part with the calculation in support, or refuse with reasons. Set the effect of the reduction, if it is owed, at the next termination date, not at the date of the request nor retroactively.
- 4Handle conciliation in the event of disagreement
If you refuse, do not reply, or grant only in part, the tenant may bring the matter before the conciliation authority within 30 days (art. 270a para. 2 CO). Keep a written record of your reply and of the increase factors set off: this is what supports your position before the authority. Conciliation proceedings are free of charge and may lead to an agreement or, failing that, to court proceedings.
1.The tenant's right and your deadline to reply
art. 270a para. 1 and 2 COThe tenant may request a reduction of the rent for the next termination date where they have reason to believe that you are obtaining an excessive return as a result of a significant change in the calculation bases, in particular a fall in costs such as a decline in the reference mortgage interest rate. The request must be addressed to you in writing.
You then have 30 days to state your position. You are under no obligation to reduce the rent spontaneously, but this deadline runs from receipt of the request, and its expiry determines the rest of the procedure.
2.The relative method and the net calculation
art. 269 et seq. CO, art. 13, 16, 17 and 18 OBLF, art. 269a let. b COThe reduction is not calculated from a historical floor, but on the change in the factors since the last valid setting of the rent. The fall in the reference rate opens a gross reduction according to the scale (about 3% per 0.25% below 5%), but the method is two-sided: in offset you set any increase factor not yet passed on since that same date.
Three families come into account: inflation up to 40% of the rise in the CPI, the increases in ordinary maintenance and operating costs actually borne, to be distinguished from value-adding works which follow the regime of additional services, and the increase reservations validly notified. A reservation does not create a quantum of its own: it merely preserves the right to invoke the factor it covers, which therefore cannot be counted twice. These factors are expressed as a percentage of the net rent and combined using one consistent method throughout the calculation. The result is the net reduction, which may be nil where these increases absorb the effect of the fall in the rate.
3.The reference rate at the last setting
art. 12a and 13 OBLFThe rate to compare is neither the building's construction rate nor the lowest rate ever reached: it is the reference rate in force at the last valid setting of the rent, that is the last increase, the last reduction or the valid initial setting. It is compared with the current rate published by the Federal Housing Office.
If the rent was set precisely at the current rate, the reduction is already built in and no reduction is owed on this ground. All factors, the fall in the rate as well as the increases set off, must be measured from this single reference date.
4.Refusal, compromise and conciliation
art. 270a para. 2 COYour reply may accept, grant in part or refuse, provided it is in writing and gives reasons. Silence does not amount to tacit acceptance, but it opens the way directly to conciliation for the tenant, just as a refusal or a partial acceptance that they do not accept.
Conciliation is never automatic: it requires the tenant to bring the matter before the authority within 30 days. Granting at least the net reduction owed, or an amount the tenant accepts, removes the dispute; a well-reasoned refusal or partial acceptance can also be defended, provided your net calculation holds. If the matter is brought, your written and figured reply constitutes your defence before the conciliation authority, then before the court where applicable.
Mistakes to avoid
Not replying offers no protection: silence immediately opens the way to conciliation for the tenant, who may bring the matter within 30 days. You lose control of the timetable and the negotiation window, without settling the dispute on the merits. Date the receipt and deal with the request without delay.
Replying to the gross figure claimed by the tenant, without setting off inflation (40% of the CPI), the cost increases and the reservations, amounts to giving up rent points you will not recover. Always place, against the fall in the rate, the column of offsetting increases not yet passed on. But each must be documented, a statement or invoice for the costs, a dated index for the CPI, a notice of reservation for the reservations: a factor set off without supporting evidence is disregarded in conciliation, your actual net reduction rises accordingly and a refusal built on unproven offsets becomes abusive.
The tenant sometimes presents a calculation going back to an old, high rate, inflating the reduction owed, whereas the rent has already been adjusted since. The point of comparison is the rate at the last valid setting, not a historical rate. If the rent was set at the current rate, no reduction is owed on this ground.
The net reduction owed takes effect at the next termination date, not at the date of the request nor retroactively. Granting an immediate or retroactive effect will not be contested by the tenant, but it costs you months of rent that nothing required. The deadline is a separate matter: letting the 30 days lapse does not undo your reply on the merits, but it makes you lose control of the timetable and opens the way to conciliation for the tenant. Set the effect at the termination date, and reply within the deadline.
Calculate the admissible net reduction
imoz reconstructs the rent history, identifies the relevant starting reference rate and calculates the admissible net reduction (gross reduction from the rate less the increases not passed on: CPI at 40%, costs, reservations). The tool then helps you frame, within 30 days, a written reply with reasons and figures, whether it accepts, refuses or grants the reduction in part.
Free, no credit card. Pricing thereafter per active lease.
Frequently asked questions
Am I required to reduce the rent?+
No. You are under no obligation to reduce the rent spontaneously; it is for the tenant to make the request in writing. But as soon as a request based on a fall in the reference rate reaches you, you must reply within 30 days, and a net reduction that is genuinely owed cannot be refused without grounds (art. 270a CO).
By how much must I reduce?+
By the amount of the net reduction, not the gross reduction. The gross reduction is read off the scale in art. 13 OBLF (about 3% per 0.25% fall in the rate below 5%), then you set against it only the justifiable increases not already passed on since the last setting. These factors combine successively on the rent, they are not subtracted in percentage points; the balance may be well below the gross reduction, or even nil. Any increase set off without supporting evidence is disregarded.
Can I offset with inflation?+
Yes. The relative method allows you to set off, in reduction of the decrease, inflation up to 40% of the rise in the CPI (art. 16 OBLF), together with the increases in maintenance and operating costs and the validly notified reservations, provided they date from after the last setting, have not already been passed on and are documented. A factor invoked without supporting evidence is disregarded in conciliation.
What deadline do I have to reply?+
30 days from receipt of the written request (art. 270a para. 2 CO). Once this deadline has passed without a reply, the tenant may bring the matter before the conciliation authority. The reply must be in writing, with reasons and figures, to preserve your position.
What happens if I refuse?+
A refusal must be in writing and give reasons. The tenant then has 30 days to bring the matter before the conciliation authority (art. 270a para. 2 CO). A refusal based on a correct net calculation can be defended; an unjustified refusal will be corrected. Conciliation proceedings are free of charge and precede, where applicable, the court.
General legal information for landlords, without the value of individual advice. imoz is a calculation and drafting-assistance tool. A contested case falls to the conciliation authority and then the court.