Rent increases in Frankfurt: rent index, cap and procedure

In Frankfurt, a rent increase to the local reference rent requires 15 months of unchanged rent at the effective date and at most 15 percent more rent in three years under the Hessian ordinance (until 25 November 2026; otherwise 20 percent, § 558 (3) BGB), modernisation and service charge increases aside. The tenant must consent.

On hardly any other topic are landlord interests and tenant protection as closely balanced as on rent increases, and hardly any is as formalised. If you know the rules, you can adjust rents with legal certainty; if you make formal mistakes, you lose months. This article summarises the position for Frankfurt (legal status: July 2026).

The basic rule: the local reference rent

In an ongoing tenancy you may demand consent to an increase up to the local reference rent (§ 558 BGB). Two time hurdles apply: the demand is permissible at the earliest one year after the last increase, and the rent must have been unchanged for 15 months at the time the increase is to take effect.

The Frankfurt rent index 2026

Since 25 June 2026 Frankfurt has had a new qualified rent index (§ 558d BGB), prepared by the Institute for Housing and Environment on behalf of the city. Qualified means: it is compiled according to recognised scientific principles and its values carry a presumption of accuracy. Courts regularly rely on them in disputes. For landlords it is therefore the strongest means of justification. The city provides the index and an online calculator free of charge; classifying your own flat correctly (age, location, fittings) deserves care, as it determines the applicable range.

The cap: 15 percent in Frankfurt

As a rule, rent may rise by at most 20 percent within three years (§ 558 (3) sentence 1 BGB). For areas in which the adequate supply of rented housing on reasonable terms is particularly at risk, the statute itself sets the figure at 15 percent; which areas those are is determined by the state governments by ordinance, for at most five years at a time (§ 558 (3) sentences 2 and 3 BGB). Hesse has issued such an ordinance, and Frankfurt is among the covered cities. It is limited until 25 November 2026; whether the reduced cap applies beyond that depends on the state renewing the ordinance or the federal legislator making the reduction permanent. Plan your increases with the 15 percent limit until then.

The procedure: consent, not decree

Legally, the rent increase is a demand for consent: you declare it in text form and justify it with one of the means in § 558a BGB: rent index, rent database, expert opinion or three comparable flats. The tenant may examine it until the end of the second month after receipt. If he consents, the new rent applies from the beginning of the third month after receipt of the demand. If he does not, you may sue for consent within three further months (§ 558b BGB). The most common sources of error are a missing or wrong justification, an incorrect rent index classification and calculation errors on the cap. Each makes the demand invalid and costs a fresh attempt.

Other routes: modernisation, stepped and indexed rent

After a modernisation the increase does not run via the rent index but as a modernisation increase under § 559 BGB: eight percent of the costs spent on the flat per year, as a unilateral declaration and without any tie to the local reference rent. It has a limit of its own in euros per square metre (§ 559 (3a) BGB), which has nothing to do with the cap in § 558 (3) BGB; the two expressly do not count into each other. How the charge is calculated, announced and declared is set out in our guide to modernisation and rent increases under § 559 BGB.

Stepped and indexed rents (§§ 557a, 557b BGB) fix adjustments in the contract; in that case an additional increase under § 558 is generally excluded. Which route fits is a contract decision at re-letting.

The rent brake on re-letting: currently contested

On re-letting, the rent brake (§ 556d BGB) limits the rent to ten percent above the local reference rent, provided a valid state ordinance designates the area. That is exactly where things currently stand in dispute: in June 2026 the Frankfurt district court declared the Hessian ordinance invalid; the ruling is not final and does not bind other courts. Until this is resolved, landlords are safest calculating new-letting rents as if the brake applied. A later claim by the tenant to recover overpaid rent is the more expensive risk.

Raising rents with good judgement

What is legally enforceable and what is economically wise are not always the same: a reliable long-term tenant is often worth more than the last notch of the rent index. In our management practice in the Rhine-Main region, assessing when and by how much an increase makes sense is part of ongoing rental management, including the formalities on which most increases fail.

Editorial responsibility: digo.immo Verwaltung & Invest - certified residential property manager under § 26a WEG (IHK Frankfurt), licence under § 34c GewO. About the certification

This article provides general information only and does not replace individual legal advice. It was created with AI assistance; the legal statements have been checked against the official texts of the law. Legal status: 26/08/2026; laws and case law may change. No warranty is given as to completeness, accuracy or timeliness. When in doubt, please seek qualified advice.