A landlord wants to bring rent closer to market value, and the tenant believes the increase exceeds the legal limit. For residential and roofed commercial leases in Turkey, this dispute is resolved under Articles 344 and 345 of the Turkish Code of Obligations (Law No. 6098). Two questions matter most: the legal cap on the increase and when and how a rent determination lawsuit must be filed.
This guide explains how rent increases are capped, how the judge sets rent when the parties disagree, the five-year adjustment rule, the mandatory mediation that has applied to lease lawsuits since 2023, and how the 3rd Civil Chamber of the Court of Cassation treated a fair-dealing reduction in a 2026 decision. You can also use our rent increase calculator.
1. The Legal Cap: Twelve-Month Average of CPI
Under Article 344/1 of the Code of Obligations, an agreement between the parties on the rent for renewed lease periods is valid only if it does not exceed the change in the twelve-month average of the consumer price index (CPI) in the previous lease year. The rule also applies to leases longer than one year.
In practice, even if the contract specifies a 50% increase, where the twelve-month average CPI change is 40%, the valid increase is at most 40%. The excess does not bind the tenant. Do not confuse this with annual inflation: the benchmark is the twelve-month average change published by TurkStat at the end of the lease year.
You can see the current rates and their effect on rent using our rent increase calculator.
2. If the Parties Cannot Agree: The Judge Sets the Rent
Where no agreement on the increase exists, rent is determined by the judge, considering the condition of the property and acting equitably, without exceeding the CPI twelve-month average change of the previous lease year (Art. 344/2).
In practice this is done through a rent determination lawsuit. The court conducts an on-site inspection, collects comparable leases and obtains an expert report. The expert determines the rent that would be paid if the property were re-let empty; the court may then apply a fair-dealing (equitable) reduction, for example because the tenant is an existing tenant.
3. Five-Year Adjustment: Can the CPI Cap Be Exceeded?
Article 344/3 provides an important exception: in leases longer than five years, leases renewed after five years, and at the end of every five years thereafter, whether or not the parties have agreed, the judge sets the rent for the new lease year. The judge takes into account the CPI twelve-month average change, the condition of the property and comparable rents.
Therefore, for long-standing tenants whose rent has only been raised by CPI, a determination close to comparable market rent is possible at the end of the fifth year. For landlords this is the only route to bring rent to true market level. Tenants should defend against such a claim with comparables, the condition of the property and proof of timely notice.
Where rent is set in foreign currency, it cannot be changed until five years have passed, subject to the law protecting the value of the Turkish currency; the hardship provision (Art. 138) is reserved.
4. When Must the Lawsuit Be Filed? The Thirty-Day Rule
Under Article 345, a rent determination lawsuit may be filed at any time. However, for the rent set by the court to bind the tenant from the start of the new lease period, one of these conditions must be met:
- The lawsuit must have been filed at least thirty days before the start of the new period, or
- The landlord must have given the tenant written notice within that time of the rent increase; in that case the lawsuit may be filed until the end of the following new lease period.
- If the contract contains a provision on a rent increase for the new period, the rent set in a lawsuit filed by the end of the new period also applies from the start of that period.
A landlord who misses the deadline can still file, but the determined rent applies from the following period. So it is important to act more than 30 days before the lease year ends.
5. Mediation Is a Condition for Lease Lawsuits
Under Article 18/B of the Mediation Law (No. 6325), added by Law No. 7445 of 28 March 2023, for disputes arising from lease relations, applying to a mediator before filing a lawsuit is a condition for the lawsuit. Provisions on eviction of leased property through enforcement without a court judgment (Law No. 2004) are outside this scope.
As a result, a rent determination lawsuit filed without a final mediation report is dismissed on procedural grounds. If the parties settle in mediation, the enforceability annotation of the settlement must be obtained from the civil court of peace. Planning the mediation timetable around the end of the lease year is critical for the 30-day rule in Article 345.
6. The Court and Procedure: Civil Court of Peace, Inspection, Expert Report
Rent determination lawsuits are heard by the civil court of peace (sulh hukuk mahkemesi); the case in the decision below was also heard there. Key elements of the proceedings:
- Inspection and comparables: Location, age, use, condition and comparable leases nearby are examined.
- Expert report: The report must be verifiable; adjustments must be made for differences between the comparables and the subject property.
- Fair-dealing reduction: It may be applied in favor of an existing tenant; the rate is set by the court on the facts.
- Appeals: Appeals to the regional court and the Court of Cassation are available.
7. Common Mistakes
Common mistakes in rent increase disputes are:
- Miscalculating the rate: The benchmark is the twelve-month average CPI change, not annual inflation.
- Missing deadlines: Not filing 30 days before the new period or not giving written notice delays the date from which the increase applies.
- Skipping mediation: It leads to dismissal of the lawsuit.
- Forgetting the five-year adjustment right: A landlord can claim a determination approaching comparable rent at the end of year five.
- Not paying rent through the bank: It creates proof problems; keep payment records.
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🧮 Related tool: You can calculate the lawful rent increase with our CPI-based rent increase calculator.
Frequently Asked Questions
For lease disputes, eviction and rent determination cases, see our Real Estate Law page, or request an appointment via our Contact page.
What is the maximum rent increase in Turkey?
For renewed lease periods, the increase cannot exceed the change in the twelve-month average of CPI in the previous lease year (TCO Art. 344/1). Even if the contract states a higher rate, the excess does not bind the tenant.
What is a rent determination lawsuit and who can file it?
It is a lawsuit for the court to set the rent. Both landlord and tenant can file it. It arises when the parties cannot agree on the increase or when the five-year adjustment period arrives (TCO Arts. 344-345).
When should a rent determination lawsuit be filed?
It can be filed at any time. For the court-set rent to bind the tenant from the start of the new lease period, the lawsuit must be filed at least thirty days before the new period, or the landlord must have given written notice of the increase within that time (TCO Art. 345).
Is mediation mandatory before a rent determination lawsuit?
Yes. For disputes arising from lease relations, applying to a mediator before filing a lawsuit is a condition for the lawsuit (Mediation Law No. 6325, Art. 18/B). Eviction through enforcement without a court judgment is outside this scope.
Can rent exceed the CPI cap after five years?
In leases renewed after five years and at the end of every five years, the judge sets a fair rent taking into account the CPI twelve-month average change, the condition of the property and comparable rents (TCO Art. 344/3). This can allow an increase approaching comparable market rent.
Does an existing tenant get a fair-dealing reduction?
The court may apply an equitable reduction to the comparable rent determined by the expert, for example because the tenant is an existing tenant. In a 2026 decision, the 3rd Civil Chamber of the Court of Cassation upheld a 10% reduction from the rent determined by the expert; the rate varies in each case.
What can a tenant do if the landlord's increase is too high?
The excess above the legal cap does not bind the tenant. The tenant can object in writing or bring a determination lawsuit, but paying only the lawful amount can create default and notice risks, so consult a lawyer before doing so. Paying through the bank and keeping records is important.