Is My Rent Increase Legal in Germany? Vergleichsmiete, Kappungsgrenze & How to Respond

Quick answer: A standard rent increase in Germany is legal only if it stays within two limits at the same time. First, the new rent may not exceed the ortsübliche Vergleichsmiete (the local comparable rent for a similar flat), which the landlord must justify with a Mietspiegel, three comparable flats, or an expert report (§558 BGB). Second, the increase may not raise your rent by more than 20% over any three-year period, only 15% in a designated tight-housing-market area (the Kappungsgrenze). Your rent must also have been unchanged for at least 15 months, and the landlord must ask in writing for your Zustimmung (consent). If a demand breaks any of these rules, the excess portion is void and you may simply refuse to pay it.

The two core limits every increase must respect

Most disputes about rent increases in Germany come down to two independent ceilings. A landlord has to clear both. Failing either one makes the demand, or at least the part that exceeds the limit, unenforceable.

1. The Vergleichsmiete ceiling (§558 BGB)

Under §558 of the Bürgerliches Gesetzbuch (BGB), a landlord may raise the rent up to, but not beyond, the ortsübliche Vergleichsmiete. This is the customary rent paid in your municipality for comparable flats regarding type, size, fittings, quality, and location, measured over the last six years. Your rent cannot be pushed above this benchmark by a normal increase, no matter how far below it you currently sit.

Crucially, the landlord bears the burden of proof. The demand letter must be justified (a Begründung) using one of the statutory instruments:

• Mietspiegel, the official municipal rent index (simple or qualified).
• Three comparable flats (Vergleichswohnungen) with named addresses and rents.
• An expert report (Sachverständigengutachten) from a certified appraiser.
• A rent database (Mietdatenbank), where one exists.

2. The Kappungsgrenze (capping limit)

Even if the Vergleichsmiete is far higher than your rent, §558 Abs. 3 BGB caps how fast you can be moved toward it. Within any three-year window, the rent may rise by at most 20%. In municipalities that a Bundesland has formally designated as having a tight housing market (Gebiete mit angespanntem Wohnungsmarkt), that cap drops to 15%. Cities such as Berlin, Munich, Hamburg, Cologne, and Frankfurt fall under the 15% rule; you should verify your own address, as designations are set by state ordinance and change over time (estimate, check your Land's current Kappungsgrenzenverordnung).

The 20%/15% is measured against the rent you paid three years ago, not against the Vergleichsmiete. This is why a tenant who is deeply below market may still only be raised a modest amount per cycle.

How to find your Vergleichsmiete

The most common and cheapest evidence is the Mietspiegel, a document published by many cities and municipalities that lists typical net cold rents (Nettokaltmiete) per square metre, broken down by year of construction, size band, and fittings. A qualifizierter Mietspiegel (qualified rent index) is prepared to recognised scientific standards and carries stronger legal weight; courts presume it reflects the Vergleichsmiete.

To use it: find your flat's construction-year band and size band, read off the range (usually a low, middle, and high value per m²), then adjust up or down within that range for features such as a modern kitchen, balcony, energy standard, or a quiet versus busy street. Multiply the per-m² figure by your living area. If your city has no Mietspiegel, the landlord must rely on comparable flats or an appraiser, both of which are harder to assemble and easier to challenge.

Worked example: is €850 legal?

Let us test a concrete case. Assume a 65 m² flat in a designated tight-market city. The figures below are illustrative estimates to show the method, always plug in your own real numbers.

Step 1, Kappungsgrenze: 15% of €700 = €105. Maximum reachable this cycle = €700 + €105 = €805.

Step 2, Vergleichsmiete ceiling: the rent may never exceed €800 regardless of the cap.

Step 3, take the lower of the two: €800 (Vergleichsmiete) is below €805 (cap), so the legal maximum is €800.00.

In this scenario you would consent to €800 and refuse the extra €50. Note that if the cap had been the binding limit (say the Vergleichsmiete were €900), the answer would flip to €805, always calculate both and take whichever is lower.

The formal rules a landlord must follow

Even a mathematically correct increase fails if the landlord ignores the procedure. A valid §558 demand must:

• Be in text form (letter or email is enough; no signature required, but it must be clearly addressed to all tenants named on the lease).
• Contain a proper justification naming the instrument used (Mietspiegel figures, the three comparable addresses, or the appraisal).
• Respect the Jahressperrfrist: the rent must have been unchanged for at least 15 months before the new rent takes effect, and a demand cannot be made until 12 months after the last increase.
• Request the tenant's Zustimmung. Unlike a modernisation increase, a §558 increase does not take effect automatically, you must agree. You have until the end of the second calendar month after receipt to respond.

If you consent, the higher rent is due from the start of the third month after the demand arrived. If you refuse and the demand was in fact lawful, the landlord can sue to compel your consent (Zustimmungsklage) within three months, so refusing a genuinely legal increase only buys time and adds risk.

Modernisation increases are different (§559 BGB)

A modernisation increase follows a separate track and is not tied to the Vergleichsmiete at all. After energy-saving or value-adding works, §559 BGB lets the landlord add up to 8% of the modernisation costs per year to the annual rent. Two caps protect tenants:

• The rent may not rise by more than €3 per m² over six years, or €2 per m² if the current rent is below €7/m² (estimate; the statutory thresholds are indexed to the flat's rent level).
• Only genuine modernisation counts; pure maintenance and repairs (Instandhaltung) must be deducted first.

Example: a €40,000 window-and-insulation upgrade allocated to a flat means up to €40,000 × 8% = €3,200 per year, i.e. about €266/month, but the per-m² cap will usually bite first. A modernisation increase takes effect automatically after the correct written announcement; your consent is not required, though you may contest the calculation or claim hardship.

What to do if your increase looks too high

1. Do not pay the higher amount yet. A §558 increase needs your consent, so paying it can itself be read as consent.
2. Recalculate both limits using your Mietspiegel and the three-year rule (our tool below does this for you).
3. Reply in writing. Consent to the lawful portion only, and refuse the excess in a dated letter. Keep proof of delivery.
4. Join a Mieterverein. A local tenants' association (or the Deutscher Mieterbund) reviews the demand cheaply and, with legal-costs insurance or membership, can push back formally.
5. Watch the clock. Respond before the end of the second month after receipt so you are not deemed silent.

Comparison: three kinds of increase

Sources

• §558 BGB, Mieterhöhung bis zur ortsüblichen Vergleichsmiete (Vergleichsmiete, Kappungsgrenze, 15-month rule, justification instruments).
• §558 Abs. 3 BGB, Kappungsgrenze 20% / 15% in tight markets.
• §559 BGB, Mieterhöhung nach Modernisierung (8% rule and per-m² caps).
• §556d BGB ff., Mietpreisbremse (Vergleichsmiete + 10% for new lettings).
• Your municipal Mietspiegel and your Bundesland's Kappungsgrenzenverordnung.

Frequently asked questions

Can I just refuse to answer a rent-increase letter?

No. Staying silent does not defeat a §558 increase. If the demand is lawful and you neither consent nor sue, the landlord can bring a Zustimmungsklage and the court can order your consent plus costs. Reply, even if only to consent to the lawful part.

How often can my landlord raise the rent?

For a standard §558 increase, the rent must have been unchanged for at least 15 months before the new rent takes effect, and the demand itself can only come 12 months after the last increase. Modernisation and operating-cost adjustments follow separate timelines.

Does the Kappungsgrenze include modernisation increases?

No. The 20%/15% cap applies to §558 Vergleichsmiete increases. Modernisation increases under §559 have their own €2-3/m² cap and are calculated independently, though they can feel like a large jump on top.

What if my city has no Mietspiegel?

The landlord must then justify the Vergleichsmiete with three named comparable flats or a certified expert report. These are harder to assemble and easier to contest, so demands in Mietspiegel-free areas are often weaker, have a Mieterverein review them.

My rent is far below market. Can it be raised to the Vergleichsmiete in one step?

Only if the gap is within the 15%/20% cap. Otherwise you can be raised only up to the cap now, and the landlord must wait out the next three-year cycle to move you closer to the Vergleichsmiete.

Reviewer note (Jonas Schneider, Versicherungsfachmann IHK): This article was checked for accuracy against the cited BGB provisions on the date of publication. Rent law, Mietspiegel figures, and tight-market designations change frequently and vary by municipality; the euro figures shown are illustrative estimates, not quotations. This is general information, not individual legal advice, for a binding assessment consult a Mieterverein or a lawyer specialising in Mietrecht.