Your tenant has been in the apartment for years. They pay on time, they cause no trouble. Then one day you see a listing for a similar flat in the same building — at twice your rent. You applied the annual increase in full every single year; how did it come to this?

In Bahçelievler, where our office is, this is one of the two situations we meet most often: apartments whose rent has fallen visibly below market simply because the same tenant stayed. And the cause is usually not a mistake the owner made — it is the increase mechanism itself.

This guide first shows, with plain arithmetic, why the gap never closes on its own; then walks through the route the law provides for exactly this problem — the rent determination lawsuit (kira tespit davası) — including the procedural details that decide such cases. And at the end, the part that gets talked about less: the situations where filing is the wrong answer.

The mechanism first: why a CPI increase cannot close the gap

Article 344 of the Turkish Code of Obligations caps the renewal-period increase at the change in CPI according to twelve-month averages. That ceiling was designed to protect the purchasing power of the existing rent — it was never designed to close a gap that has already opened between you and the market.

The reason is simple arithmetic. Percentages operate on absolute amounts: apply the same rate to a low base and a high base, and the distance between them does not shrink — it grows.

Lagging rent Comparable market rent Gap
Today TL 15,000 TL 30,000 TL 15,000
After the same 30% increase TL 19,500 TL 39,000 TL 19,500

The figures in the table are not a market claim — they are chosen only to show the mechanism. The point is this: when both apartments receive the same legal increase, the lagging one falls a little further behind every year. Repeat it for ten years and nothing changes.

There is also a historical reason this picture is so common in Istanbul. Between June 2022 and July 2024, residential rent increases were capped at 25% regardless of inflation. Inflation ran far above that rate through the period, so a large share of apartments that happened to be tenanted then lost ground in real terms for two straight years — and never caught up. How the legal ceiling is calculated, and which month's data applies, is covered in our guide to Turkey's legal rent increase cap; the rate itself is published monthly by TurkStat.

"Five years have passed — can I now demand whatever I want?"

No — and this is the point on which landlords most often get it wrong.

Completing five years does not give you the right to impose a new rent unilaterally. If you notify your tenant that "the fifth year is up, the rent is now X", the amount they legally owe — unless they agree — is still the old rent plus the CPI-capped increase. And they are not in default for refusing to pay the difference.

What the five-year mark actually changes is this: beyond that threshold, a judge setting the new rent is no longer bound by the CPI ceiling. The relevant paragraph of Article 344 provides that for tenancies longer than five years, or renewed after five years — and at the end of every five years thereafter — the rent is to be set equitably, having regard to the twelve-month-average CPI change, the condition of the property and comparable market rents. The index becomes just one of three criteria.

Three details matter:

  • The five years count from the start of the tenancy relationship as a whole, extension years included — not the contract's initial term. A one-year contract signed in 2019 that renewed automatically each year passed the five-year mark in 2024.
  • Whether or not your contract contains an increase clause changes nothing here. With or without one, a determination can be sought after five years.
  • The statute speaks of the end of the fifth year and the end of every five years after that. Whether the same freedom applies in the years in between is contested in practice; it is a question decided on your specific dates, and one of the first things to ask a lawyer before filing.

If you want to read the statute yourself, the full Turkish Code of Obligations is available at mevzuat.gov.tr.

What the rent determination lawsuit is — and is not

A rent determination lawsuit asks the court to set the rent for the new period. It exists for the moment the parties cannot agree, and it ends with the court fixing the monthly rent, as a number, for the rental period in question.

Let us be equally clear about what it is not, because these get mixed up constantly:

  • It is not an eviction case. Winning does not remove the tenant; they stay, paying the new rent. Eviction rests on separate grounds and separate procedures — our guide to evicting a tenant in Turkey covers those. Do not treat the two as interchangeable tools.
  • It does not recover past years' losses in one sweep. The determination takes effect for the rental period the case is tied to; it does not let you collect five years of foregone rent retroactively.
  • A procedural note: in disputes arising from tenancies, applying to mediation first is a precondition of filing, and rent determination claims are treated as falling within it in practice. A case filed directly can be dismissed on procedure. The mediation stage is also where many files end without ever reaching a courtroom — the parties agree on a stepped increase and close the matter. That is not a bad outcome; it is often the fastest one.

Notice timing: the detail that decides the case

A rent determination lawsuit can be filed at any time. But which period the court-set rent applies from hangs on a single step taken before filing. Article 345 draws this line, and it is where landlords make their most expensive mistake.

For the new rent to bind the tenant from the start of the new rental period, one of the following must be true:

  1. The case was filed at least thirty days before the new period begins; or
  2. The landlord gave the tenant written notice that the rent would be increased, at least thirty days before the new period begins — in which case the case may be filed any time up to the end of that new period; or
  3. The contract itself contains a clause providing for an increase in the new period — in which case a case filed by the end of the period also takes effect from its start.

In practice this means: put your rental year's start date in the calendar, and send the notice at least a month before it. Send it a week late, with no increase clause in the contract, and the judgment you win may only bite from the following period — a full extra year at the old rent.

Sending the notice through a notary is the standard for proof. State the current rent, the start date of the new period, and that you are asking for the rent to be re-determined. Which of the three routes fits your contract depends entirely on its text and its dates — so have a lawyer confirm before the notice goes out. A one-day error here cannot be repaired afterwards.

If you own from abroad and a manager runs your tenancy, this notice calendar is precisely the kind of deadline they should be tracking for you — it is part of what property management for remote owners is for.

What evidence actually decides the figure

This is the heart of the case. The court does not pluck a number from the air: it holds an inspection, takes an expert report and examines comparable rents. In practice, the weight falls on:

  • Actual lettings nearby. Amounts in signed contracts — not listing prices. Listings show the pre-negotiation figure and count as weak evidence on their own.
  • The property's own condition. Building age, floor, aspect, net area, heating, lift, parking, whether it is in a managed complex, state of repair. Two apartments on the same street can diverge seriously on these items.
  • What the tenant contributed. Permanent improvements the tenant made at their own cost can become a point of argument in the determination.
  • Whether the comparable is truly comparable. A flat in a different neighbourhood, of a different age or type, does not qualify. The quality of the comparables in the file directly shapes the outcome.

One more thing that surprises landlords: courts generally do not adopt the comparable market level as-is. They apply an equity discount for the sitting tenant, on the reasoning that a long-standing tenant gives the owner stability and payment security. There is no fixed percentage; it varies with the judge's discretion and the strength of the comparable evidence. Do not expect the judgment to land exactly on today's market rent.

The most useful thing to do before filing is to learn your property's current, comparables-based market rent. It sets your claim at a realistic level — and it raises the odds of settling with your tenant without a courtroom; a free valuation exists to close exactly that gap. Cases filed on guesswork waste time.

Time, cost and honest expectations

We will not promise you a duration here, because any number would mislead. How long a rent determination case takes depends on the mediation stage, the court's workload, the inspection calendar, objections to the expert report and a possible appeal — variables neither we nor you control. Two similar files in the same courthouse routinely finish at different speeds. What follows is not a schedule but the structural facts:

  • While the case runs, the tenant keeps paying the old rent. Nothing changes in your collections until judgment.
  • When judgment comes, the difference has accrued and can be claimed for the relevant period — but a rent determination judgment must become final before it can be enforced. The judgment date and the date money reaches your account are not the same date.
  • The cost items are filing and judgment fees, the inspection and expert advance, and counsel's fee. Because the case value is computed on the annual rent difference, suing over a small gap rarely pays for itself.

That last point deserves underlining: if the gap is small, the case is economically pointless. Unless a year's difference clearly exceeds the estimated costs and the time you will spend, one of the alternatives below is almost always the better answer.

Before five years: is an adaptation lawsuit a way through?

The only theoretical route to lift the rent above the index ceiling before five years is an adaptation claim under Article 138 — excessive hardship. That provision applies when an extraordinary, unforeseeable event upsets the balance of the contract to an unbearable degree.

The honest answer: courts are reluctant to accept this route for residential rents. Inflation tends to be treated as foreseeable in Turkey's conditions, and the legislature has already provided a dedicated mechanism for rent increases (Article 344). Adaptation claims are argued mainly in long-term, special-condition contracts — foreign-currency leases, long commercial terms. Before forcing this door for an ordinary residential tenancy short of five years, have a lawyer assess whether your file genuinely has something exceptional in it.

The lawsuit is not always the answer: three alternatives

As an agency it would be easy to tell you "assert your rights, file the case." What we actually see in the field is that for a large share of owners, the out-of-court routes are faster and cleaner.

1. A renewal negotiation and a stepped increase

A tenant who has stayed for years, paid on time and kept the apartment well gives you something invisible but real: zero vacancy, zero refurbishment, zero tenant-search cost. Sitting down and agreeing a plan that closes the gap over two or three years — this much this year, this much next — removes both the litigation cost and the uncertainty.

Make the argument numerical, not emotional: here is the comparable rent, here is yours, here is the gap. The tenant's alternative is moving, and moving costs them too. And when weighing how hard to push, count the empty months you would risk — the table in the true cost of an empty apartment shows that one vacant month usually exceeds several months of the difference you are arguing over.

2. An agreed eviction undertaking

If your tenant is already thinking of moving, there is an arrangement where both sides win: a fixed move-out date in exchange for the rent staying unchanged until then. It is secured with a properly executed written eviction undertaking (tahliye taahhütnamesi), and when the date arrives the apartment is re-let at market rent.

The validity conditions are strict — the tenant must sign it personally, it cannot be dated the same day as the lease, the move-out date must be definite — and the window for acting once the date passes is short. The details and deadlines are in evicting a tenant in Turkey. This document works when it is given by genuine agreement, not under pressure.

3. Selling

In some files the rational decision is to exit. An apartment with a sitting tenant on below-market rent holds little appeal for a buyer who wants to live in it — but the picture is different for an investor running the numbers, because what matters to them is not today's rent but the date the rent can be re-set.

Put the return from holding next to the sale price before deciding. Our rental yield calculator shows in a few minutes where your apartment's gross yield and payback period stand against its sale value. If price-to-rent multiples in your district have climbed, the cost of holding at a low rent may be larger than you think.

Which route fits which situation

Situation Sensible route Watch out for
Tenancy under 5 years CPI-capped increase + renewal negotiation Adaptation claims rarely succeed at this stage
5 years done, large gap, tenant won't negotiate Rent determination lawsuit Notice timing and comparables decide the case
5 years done, moderate gap Agreed stepped increase Litigation costs can swallow the difference
Tenant already considering moving Eviction undertaking + re-letting Strict formal requirements, short deadlines
Little appetite to keep the property Sale With a sitting tenant, the buyer profile changes

The pairings in the table are a compass, not a legal assessment of your file; for certainty, put your contract and your dates in front of a lawyer.

One last practical note: whichever row you are in, the first step is the same. Without a comparables-based figure for your apartment's current market rent, you cannot ground a claim, negotiate with your tenant or judge a sale sensibly — start with a free valuation. And if you would rather not track the renewal calendar, the notices and the yearly increase yourself, that is part of what we take over — the scope is on our services page. The cheapest way to stop the gap ever growing this large again is to pause once a year, at renewal, and look.