In short: In commercial lease law, the lease agreement determines when and how an index rent changes. There is no statutory lock-in period like for residential premises. The clause must comply with the requirements of the Price Clause Act; if it is a general business condition imposed by the landlord, it must also withstand review by the AGB control board. If it fails to meet these requirements, it is null and void from the outset, according to the BGH judgment of March 11, 2026 (XII ZR 51/25).
Tenants should therefore check the basis for already paid increases. Renters should in particular review the reference month and the adjustment mechanism in their terms and conditions.
At a glance
- Legal basis: Contract and Price Clause Act (PrKG); § 557b BGB does not apply to ordinary commercial space rental agreements.
- Acceptability: The clause must be linked to an acceptable consumer price index, and one of the long-term obligations of § 3 PrKG must be present, such as a landlord’s right to terminate the lease or a tenant’s right to renew the lease for a total of at least ten years.
- Time limit: Only if it is agreed upon in writing.
- PrKG and AGB law to be examined separately: A mere breach of the PrKG only becomes legally binding after a final determination (§ 8 PrKG); a breach of the GTC renders the clause ineffective from the outset (BGH, judgment of 11 March 2026, XII ZR 51/25).
- In the BGH case, the following is objected to: a reference month more than two years before the start of the lease and a contradictory adjustment mechanism.
What is an index rental in a commercial lease agreement?
In the case of an index rental, the rent is linked to a price index, usually the German Consumer Price Index (VPI) of the Federal Statistical Office. If the index rises or falls, the rent changes in accordance with the agreed ratio. This is also known as a value protection clause, sliding clause or index clause. Often, the index clause only covers the net rent. Whether additional rental components are included depends on the contract; advance payment of operating costs and their billing are to be considered separately.
In addition to the actual index clause, there are other adjustment mechanisms that are exempt from the prohibition in § 1, paragraph 1 of the PrKG (Section 1, paragraph 2 of the PrKG):
- Performance commitment: The index change triggers a new rent adjustment, which involves a genuine discretion and must be carried out in a fair manner. However, if the new amount is determined mathematically, there is no performance clause, even though one party only has to declare the adjustment.
- Dispute clause: The rent follows the development of similar or comparable services, not an overall price index.
It is important to distinguish between the pure New renegotiation clauseThe parties merely agree to negotiate the rent in the event of certain changes. It does not fall under the prohibition of § 1, paragraph 1 of the PrKG, because they do not automatically change the rent but only arrange for negotiations.
Difference from residential rental
Regulates for living space Section 557b of the German Civil Code the index rent explicitly: The rent must, apart from statutory exceptions, remain unchanged for at least one year at a time; the change must be claimed in writing and paid from the following month after receipt. For ordinary business premises, see Section 578(2) of the German Civil Code (BGB) Not under § 557b BGB. A special case is governed by § 578, paragraph 3, BGB for certain rentals for residential purposes. Otherwise, these protection rules apply to the commercial sector only if the parties agree on them.
When is an index clause in a commercial lease permissible?
The Price Clause Act generally prohibits automatic price adjustments and allows them only in certain cases. For commercial lease agreements, the following applies: § 3 PrKG especially on two points:
- Allowed index: the consumer price index of the Federal Statistical Office or a Statistical State Office, or a consumer price index determined by the Statistical Office of the European Union (Eurostat).
- Long-term commitment: The law lists several alternatives. In particular, the duration from the conclusion of the contract to the due date of the last payment, a refusal by the landlord to provide the necessary documents, and the possibility of terminating the contract are to be examined. ordinary cancellation for at least ten years and a right for the tenant to extend the contractual term to at least ten years. Therefore, a fixed initial term of ten years is not the only way; a five-year fixed term with a unilateral option for the tenant to extend the term by five years may also suffice.
In addition, the clause must be sufficiently specific and may not unfairly disadvantage any party (§ 2 PrKG). According to § 2, paragraph 3 of the PrKG, problems arise in particular from clauses that only provide for increases but not reductions, that only allow one side to request an adjustment, or that could lead to an unreasonable change.
If a clause violates the price clause law, it will be nullified according to Section 8 PrKG Only with the definitive determination of invalidity, namely for the future, unless an earlier invalidity has been agreed upon. Up to that time, any increases paid cannot be regularly claimed on this basis.
Form of the rental agreement
In the case of commercial space rental agreements with a term of more than one year, the written form must be observed in accordance with § 578, paragraphs 1 and 2, in conjunction with § 550 BGB. For old contracts, an interim regulation that has now expired (Art. 229 § 70 EGBGB) still applies. A formal defect does not invalidate the contract, but may lead to it being considered concluded for an indefinite period. This can also eliminate the long-term commitment required for the index clause. Implementing an already agreed automatic index clause does not require a separate contract amendment. However, if the parties agree on a new rental rate or change the index clause themselves, this may trigger the statutory text form requirements for long-term commercial lease agreements. Additionally, contractual form requirements for notification of adjustments must be observed.
BGH 2026: When index clauses are invalid
For a long time, it was debated whether a formal index clause would also be examined under the law of contractual terms and conditions, in addition to the price clause law. The Schleswig Higher Regional Court had applied the special rule of § 8 PrKG also to transparency deficiencies (order of 05.02.2024, 12 U 69/23). The Higher Regional Court of Düsseldorf saw things differently (judgment of 05.06.2025, I-10 U 146/24). The Federal Court of Justice has resolved the issue by Judgment of March 11, 2026 (XII ZR 51/25) In the sense of the Düsseldorf Higher Regional Court: The price clause law and the terms and conditions of contract law apply in parallel; § 8 PrKG does not override the terms and conditions of contract control. However, a violation of the price clause law is not automatically also a violation of the terms and conditions of contract; both standards must be examined separately.
If it is an General Terms and Conditions set by a contracting party, in particular: § 307 BGB To be noted. In contracts between entrepreneurs, the special features of § 310, paragraph 1, of the German Civil Code apply. Individually negotiated arrangements must be assessed separately. If the clause is invalid under § 307 of the German Civil Code, it is void from the outset; the remaining rental agreement remains generally valid (§ 306 of the German Civil Code).
What was challenged in the final case
The lease agreement for the premises for a physiotherapy practice was concluded on August 28, 2019, began on September 1, 2019, and ran for at least ten years. The clause was based on the index value from May 2017. This shifted price increases from more than two years before the lease began to the tenant, who was unable to use the premises during this time. In addition, the adjustment mechanism was contradictory: the rent was to change automatically, but the increase would only take effect after written request; the point of reference for later adjustments remained open as well.
This assessment comes from the previous court and was confirmed in the BGH proceedings; the appeal did not challenge it, but primarily concerned the legal consequence. This does not imply a general ban on any reference month before the start of the lease. However, such a reference month can be problematic if it results in price increases from a period without corresponding rental use being transferred to the tenant.
What the judgment does not mean
The judgment does not invalidate all index clauses. Whether a specific clause is affected depends on its wording, its creation, and the date of the rental commencement.
When is the index rental adjusted?
The law does not require a specific adjustment schedule for the industry. Typical contractual check points are:
- Reference index: What index level is the starting point, and is it before or after the rental begins?
- Threshold value: Many clauses require an adjustment only when the index has changed by a certain percentage or a number of index points. Percentage adjustments are easier to handle when switching to a new base year than point adjustments (Destatis).
- Follow-up adjustments: Does the adjusted index used in this case serve as a new reference point?
- Effectiveness: Does the rent change automatically, or only by declaration? A notification requirement does not render an automatic clause ineffective. However, the creation of the claim, the due date, and the information obligations must be clearly separated from each other. The BGH case was particularly concerned with the confusion.
Recourse to the past
If the rent changes automatically after the contract, the landlord can generally demand increased fees retroactively. Limits are set by the regular statute of limitations under §§ 195, 199 BGB and, in exceptional cases, the enforcement thereof. If the clause requires a declaration, the higher rent will only take effect from the date stipulated in the contract.
Calculating index rents in the commercial sector
The basic formula is: New rent = previous rent × new index value ÷ corresponding reference index. The reference rent and the reference index must match each other, and all index values must come from the same index series with the same base year. For calculation, the unrounded ratio should be used, not a rounded percentage. Instructions for calculation are provided in the Federal Statistical Office.
Example (fictitious)
The basic rent is 4,000 € per month. The clause provides for an automatic adjustment as soon as the VPI % changes by at least 5% compared to the reference index. Additionally, for the example it is assumed that after each adjustment, the index value used is considered the new reference point for the next threshold test. All index values come from the same index series and the same base year.
The index rises from 118.0 to 124.0 points, that is about 5.08 %%. The threshold has been reached. New rent: 4,000 € × 124.0 ÷ 118.0 = 4,203.39 €. For the next adjustment, 4,203.39 € and 124.0 points are the new reference values.
Is there a waiting period for index rents in commercial premises?
No, at least not a statutory one. However, the parties can agree that the rent will remain unchanged for a certain period of time or only adjusted at fixed intervals. In the 2026 BGH case, the rent was initially agreed upon for 24 months. If such a provision is missing, the rent can change as soon as the contractual requirements are met.
A statutory right of increase under § 558 BGB does not exist in the case of ordinary commercial space rental agreements. An adjustment usually requires an effective contractual basis or a new agreement. Statutory exceptions, in particular the disruption of the business basis after § 313 BGB, They remain unaffected. A cancellation alone does not increase the rent.
Ineffective index clause: Recovery of paid increases
If the index clause is invalid from the outset due to a breach of the terms and conditions, the tenant has paid the increase amounts without any legal basis. The basis for claiming reimbursement is generally Section 812, paragraph 1, sentence 1, Alt. 1 of the German Civil Code. Whether and to what extent a reimbursement is enforceable also depends on statute of limitations and possible objections, such as § 814 BGB in the event of positive knowledge of non-guilt; mere payment or mere doubts do not constitute such knowledge.
The regular statute of limitations is three years. It generally begins with the end of the year in which the claim arose and the legal knowledge requirements are met (Section 199(1) of the Civil Code (BGB)). The 2026 BGH ruling does not automatically trigger a new deadline for all previous payments.
For the examination, the following is required: the rental agreement and any addenda, all increase notices, an overview of the amounts actually paid, and the index values used.
Residential and commercial space compared
| Question | Living space | Commercial space |
|---|---|---|
| Legal basis | Section 557b of the German Civil Code | Contract, price clause law; in the case of clauses submitted, additionally § 307 BGB |
| Long-term commitment | Not required | One of the alternatives provided for in § 3 PrKG, such as the right to terminate the contract or the right to extend it for at least ten years |
| Time limit | One year, with statutory exceptions (§ 557b, paragraph 2, BGB) | Only if agreed upon in writing |
| Assertion | Statement in written form; payment due from the following month (§ 557b, paragraph 3, BGB) | After the contract: automatically or by declaration |
| Result of a defect | Ineffectiveness under the German Civil Code | Simple PrKG violation: generally subject to a final judgment; breach of the terms and conditions: from the outset |
Here's how to check your index clause
The following points serve as a starting point. A single characteristic does not automatically lead to a conclusive result.
- Clear up the duration and form. Is one of the long-term obligations under § 3 PrKG present? Does the contract meet the prescribed form requirements?
- Check the index. Is an admissible consumer price index used?
- Compare the reference month to the start of the rental period. Will price increases from a period before the rental period be passed on to the tenant?
- Check for both sides. Does the rent also fall with a falling index?
- Read the mechanism. Is it clearly specified whether the adjustment is made automatically or by declaration and from which index level future adjustments are calculated?
- Clarify the origin of the clause. Was the clause put in place by a party, perhaps from a model contract, or negotiated individually?
- Document payments. Retain information about which increases have been paid since when.
Frequently asked questions
Does the rent in commercial premises have to remain unchanged for at least one year?
No, not by law. § 557b BGB does not apply to ordinary commercial space rental agreements. A waiting period or fixed adjustment intervals only apply in the commercial sector if they are agreed upon in the rental agreement.
Can I claim back paid index increases as a tenant?
Yes, under certain conditions. If the clause is invalid due to a breach of the terms and conditions, it is invalid from the outset (BGH, XII ZR 51/25), and the increases can be claimed back in accordance with § 812 BGB. Enforcement is only possible within the limitation period and subject to possible objections. In the case of a mere PRKG breach, the invalidity generally only takes effect upon a final determination.
Is an index clause invalid if the contract runs for less than ten years?
Not without a certain degree of certainty. A fixed initial term of less than ten years does not preclude an allowable index clause. In particular, the duration until the last payment, a sufficiently long period of notice by the landlord and the tenant’s right to extend the lease are to be examined. If a relevant exception to the price clause prohibition is absent, the legal consequence of a mere PrKG violation is governed by § 8 PrKG.
Can the landlord claim for overlooked increases?
Yes, if the rent automatically adjusts according to the contract, subject to the statute of limitations and in exceptional cases by enforcement. If the clause requires a declaration, the increase will only take effect at the time stipulated in the contract.
Will the ancillary costs be indexed as well?
Often not. Many clauses only cover the net rental price; the contract is decisive. Prepayments for operating costs and their billing must be examined separately.
Do you want to have your index clause checked?
We review index clauses in existing commercial lease agreements, quantify potential claims, and advise landlords on the drafting of new clauses. For a non-binding contact, please reach us by phone, email, or via the contact form.
- Telephone: 0221 - 801 87 670
- E-Mail: info@mth-partner.de
Law firm Tieben
Sachsenring 34
50677 Cologne
Read more
- Service charge statement in commercial tenancy law: deadlines, receipts and audit – which can be charged in addition to the basic rent.
- Higher Regional Court of Munich: Obligation of the acquirer to sign long-term commercial lease agreements – why the duration of the lease remains important even when the owner changes.
- Tenancy law in Cologne – Advice and representation in residential and commercial lease law.
This article provides a general overview and does not replace a legal assessment of the individual case.
