Purpose
The rent increase up to the local comparative rent is strict as to form and two-sided: the same review program determines whether the landlord holds an enforceable demand in hand and whether the tenant must consent. A demand that is defective as to form is invalid — the obligation to consent does not arise, the consideration period does not begin to run, and the landlord ultimately loses at least one year. This skill runs both perspectives through the same review cascade and at the end quantifies the actually permissible increase amount.
Inputs
- Perspective: landlord draft or tenant review of a received demand
- The demand in its wording (for tenant review), date of receipt, form (letter / email / text form)
- Current net cold rent and date of the last rent increase or of the start of the lease
- Apartment area, residential location, year of construction, fittings, energy-related condition
- Means of justification: municipal rent index / expert opinion / three comparable apartments / rent database
- Earlier increases in the last three years (for the cap limit)
- Is the location a rent brake area (Section 556d of the German Civil Code (BGB), state-law ordinance)?
Sub-agent architecture
The review is carried in prose by specialized steps; this skill deliberately does not include a agentsblock is deliberately omitted by this skill (mietrecht convention). A form reviewer first assesses solely the validity of the demand — text form, addressing, means of justification, specificity — without any regard to the amount. Only once the demand is valid as to form does a substantive reviewer assess the demanded rent against the local comparative rent and the cap limit. A deadline reviewer checks the annual blocking period, the 15-month period, the consideration period and the litigation period. A demarcation reviewer examines across the board whether in truth a modernization rent increase under Section 559 of the German Civil Code (BGB) is present, which follows a different regime. The most common source of error — conflating the question of form with the question of merits — is structurally excluded by this separation.
Procedure
0. Determine perspective (landlord draft / tenant review)
The review material is identical, the direction of view is not. Landlord draft: Steps 1–7 are read as drafting requirements — each point is a requirement that the draft must satisfy before it leaves the house. The result is a ready-to-send demand plus a deadline calendar. Tenant review: The same steps are read as points of attack — each point is a possible ground for invalidity. The result is a recommendation to consent (full / partial / refuse) plus a litigation risk assessment. In the tenant review, the strict order applies: form before amount: if the demand is invalid as to form, the amount no longer needs to be examined at all. From the landlord's perspective, conversely, the amount should be established early because it governs the choice of the means of justification.
1. Waiting period and annual blocking period (§ 558(1) BGB)
The landlord may demand consent to a rent increase if the rent at the time of taking effect of the increase has remained unchanged for 15 months (15-month period). The demand itself may be received no earlier than 12 months after the last rent increase (annual blocking period). The two periods must be distinguished: the annual blocking period concerns receipt, the 15-month period concerns validity. Increases under §§ 559–560 BGB (modernization, operating costs) are disregarded in the calculation. If the last increase was less than one year ago, the demand is premature and invalid.
2. Local customary comparative rent (§ 558(2) BGB)
Decisive are the amounts agreed or amended in the municipality or a comparable municipality for non-price-controlled housing of comparable type, size, fittings, condition and location, including energy-related fittings and condition in the last six years . In practice, the rent demanded is checked for plausibility against the relevant rent index figure: correct field, correct range, valid version. For the area figure, the actual living area is decisive, not the one stated in the contract (BGH, judgment of 18.11.2015 – VIII ZR 266/14, https://dejure.org/dienste/vernetzung/rechtsprechung?Gericht=BGH&Datum=2015-11-18&Aktenzeichen=VIII%20ZR%20266/14). If the demand is above the range, it is unfounded as to amount to the extent that it exceeds the local customary comparative rent.
3. Cap limit (§ 558(3) BGB)
Irrespective of the local customary comparative rent, the rent may within three years increase by no more than 20% . In areas with a threatened housing supply, a reduced cap limit of 15%applies by state-law ordinance. Calculation: the starting figure is the rent three years before the increase takes effect; interim increases under § 558 BGB are counted cumulatively. Increases under §§ 559–560 BGB are disregarded. If the demand exceeds the cap limit, it is effective only up to the limit ; the excess part is eliminated but may be demanded again later.
4. Means of justification (§ 558a BGB)
The demand must be justified; one of the four statutory means suffices, but it must be specific :
- Rent table of the municipality — simple or qualified (Section 558d of the German Civil Code). When referring to it, the relevant field and range must be named and the apartment specifically classified; a general reference to "the rent table" is notsufficient. For a qualified rent table, the presumption of Section 558d(3) of the German Civil Code applies; it lapses if the rent table has not been adjusted after two years (Section 558d(2) of the German Civil Code).
- Expert opinion of a publicly appointed or officially recognised qualified expert — with a comprehensible derivation, not just the result.
- Three comparable apartments with location, size, furnishings and specific comparative rent — determined in such a way that the tenant can find and verify them.
- Rent database (Section 558e of the German Civil Code).
If a permissible justification is missing or is too indefinite, the request is ineffective — no obligation to consent arises.
5. Form and addressing (Section 558a(1) of the German Civil Code, Section 126b of the German Civil Code)
- Text form under Section 126b of the German Civil Code: a legible declaration on a durable medium, naming the person making the declaration. Email is sufficient; an oral notice is not.
- From all landlords to all tenants: A request to only one of several tenants is ineffective. In the case of representation, the power of attorney must be enclosed (Section 174 of the German Civil Code), otherwise rejection is imminent.
- Definiteness of the demand: expressly state the old rent, the new rent, the difference and the point in time at which it takes effect.
- Recommendation: make receipt provable by registered mail with proof of delivery or by courier with a witness.
6. Consent period and action for consent (Section 558b of the German Civil Code)
The tenant has until the end of the second calendar month after receipt to consent (consideration period). If he consents, he owes the increased rent from the beginning of the third calendar month after receipt. If he refuses or remains silent, the landlord can within three further months sue for consent (Section 558b(2) sentence 2 of the German Civil Code); if he misses this time limit for action, he must start the entire proceedings anew. If the request is only partially justified, the tenant should consent to the extent of the effective part in order to avoid an action in that respect.
7. Distinction from the modernisation rent increase (Section 559 of the German Civil Code)
An increase under Section 559 of the German Civil Code follows a different regime: It is based on modernisation measures carried out, operates as a unilateral declaration of intent without consent of the tenant, has its own cap (Section 559(3a) of the German Civil Code) and is not bound to the local comparative rent. Check whether the letter is actually a demand under Section 558 of the German Civil Code or covertly contains a modernization rent increase. Mixing both routes in one letter or including modernization-related amounts in a Section 558 demand is defective and must be separately challenged. Further detail: /mietrecht:modernisierung-559-bgb.
8. Rent brake and permissible increase amount (Section 556d of the German Civil Code)
In rent brake areas, Section 558 of the German Civil Code continues to apply; the limitation to the local comparative rent plus 10% concerns re-letting, not the ongoing increase. However, check whether the initial rent itself is excessive under Sections 556d et seq. of the German Civil Code and has been challenged — then the challenged, reduced rent is the starting value. Further detail: /mietrecht:mietpreisbremse.
Permissible increase amount — final calculation: the minimum of (a) the local comparative rent and (b) the initial rent plus the cap limit. The demand is mirrored against this value; the difference is the unfounded part.
Deterministic calculation
The time limits under Section 558 of the German Civil Code are event-based periods under Section 187(1) of the German Civil Code; the end of the period shifts under Section 193 of the German Civil Code to the next working day. The calculator in ../../../scripts/legal_calc/ does only the arithmetic — the date of receipt and the date of the last increase remain legal inputs and must be separately proven.
# 15-Monats-Frist: letzte Erhöhung wirksam ab 01.01.2025
python -m scripts.legal_calc.cli frist --ereignis 01.01.2025 --menge 15 --einheit monate --land BY
# Jahressperrfrist § 558 Abs. 1 S. 2 BGB: frühester Zugang eines neuen Verlangens
python -m scripts.legal_calc.cli frist --ereignis 01.01.2025 --menge 12 --einheit monate --land BY
# Überlegungsfrist § 558b Abs. 2 BGB: Zugang 15.01.2026, Ende zweiter Kalendermonat
python -m scripts.legal_calc.cli frist --ereignis 15.01.2026 --menge 3 --einheit monate --land BY
# Klagefrist des Vermieters: 3 Monate ab Ablauf der Überlegungsfrist
python -m scripts.legal_calc.cli frist --ereignis 31.03.2026 --menge 3 --einheit monate --land BY
--json provides the calculation steps together with the statutory citation in machine-readable form. The consideration period under Section 558b of the German Civil Code is a calendar month period, not a pure monthly period — the calculator result must be checked against the wording ("expiry of the second calendar month after receipt").
Sources
Statutes
- Section 558 of the German Civil Code, Section 558a of the German Civil Code, Section 558b of the German Civil Code, Section 558c of the German Civil Code, Section 558d of the German Civil Code, Section 558e of the German Civil Code
- Section 559 of the German Civil Code (modernization rent increase), Section 556d of the German Civil Code (rent brake)
- Section 126b of the German Civil Code (text form), Section 174 of the German Civil Code (presentation of power of attorney)
- Section 187 of the German Civil Code, Section 188 of the German Civil Code, Section 193 of the German Civil Code (calculation of time limits)
Commentaries
- Börstinghaus, in: Schmidt-Futterer, Mietrecht, 15th ed. 2023, Section 558 of the German Civil Code marginal no. 1 et seq.
- Eisenschmid, in: Schmidt-Futterer, Mietrecht, 15th ed. 2023, Section 558a of the German Civil Code marginal no. 1 et seq.
- Artz, in: MüKoBGB, 9th ed. 2023, Section 558 marginal no. 1 et seq.; Section 558a marginal no. 1 et seq.
- Weidenkaff, in: Grüneberg, BGB, 84th ed. 2025, Section 558 marginal no. 1 et seq.
Case law
- German Federal Court of Justice, judgment of 18.11.2015 – VIII ZR 266/14 (rent increase in case of living area discrepancy; actual area is decisive, cap limit remains) — verified: https://dejure.org/dienste/vernetzung/rechtsprechung?Gericht=BGH&Datum=2015-11-18&Aktenzeichen=VIII%20ZR%20266/14
- German Federal Court of Justice, judgment of 23.06.2010 – VIII ZR 256/09 (implied living area agreement) — verified: https://dejure.org/dienste/vernetzung/rechtsprechung?Gericht=BGH&Datum=2010-06-23&Aktenzeichen=VIII%20ZR%20256/09
- For the depth of reasoning and specificity of the three comparable apartments, the relevant BGH case law must be consulted
[unverifiziert - prüfen]. Do not adopt any case number without verifying it yourself in juris / Beck-Online.
Drafting aid — rent increase request (§§ 558, 558a BGB)
Sehr geehrte Frau …, sehr geehrter Herr …,
hiermit verlange ich Ihre Zustimmung zur Erhöhung der Nettokaltmiete für die
von Ihnen gemietete Wohnung <Anschrift, Lage im Haus>.
Die derzeitige Nettokaltmiete beträgt <Betrag> EUR monatlich. Sie ist seit
dem <Datum> unverändert. Ich verlange die Zustimmung zur Erhöhung auf
<Betrag> EUR monatlich, mithin um <Differenz> EUR.
Zur Begründung nehme ich Bezug auf den Mietspiegel der Stadt <Ort> in der
Fassung vom <Datum>. Die Wohnung ist dort in das Feld <Feld> einzuordnen
(Baujahr <…>, Wohnfläche <…> m², Ausstattung <…>, Lage <…>). Die Spanne
dieses Feldes reicht von <…> EUR/m² bis <…> EUR/m²; der Mittelwert beträgt
<…> EUR/m². Die verlangte Miete liegt mit <…> EUR/m² innerhalb der Spanne.
Die Kappungsgrenze des § 558 Abs. 3 BGB ist gewahrt: Die Miete betrug am
<Datum, drei Jahre zuvor> <Betrag> EUR; die Erhöhung beträgt <…> % und liegt
damit unter <20 % / 15 %>.
Sie können der Erhöhung bis zum Ablauf des zweiten Kalendermonats nach
Zugang dieses Schreibens zustimmen. Die erhöhte Miete ist ab dem <Datum>
zu zahlen.
Mit freundlichen Grüßen
Output format
MIETERHÖHUNG § 558 BGB — <Vermieter-Entwurf / Mieter-Prüfung> — <Mandat-ID> — <Datum>
I. Perspektive [Vermieter-Entwurf / Mieter-Prüfung]
II. Form (§ 558a Abs. 1, § 126b) [✅ / ❌]
- Textform [✅ / ❌]
- Alle Vermieter / alle Mieter [✅ / ❌]
- Bestimmtheit der Forderung [✅ / ⚠️]
III. Begründungsmittel (§ 558a) [Mietspiegel / Gutachten / 3 Wohnungen / Datenbank]
Bestimmtheit [✅ / ⚠️ / ❌]
IV. Fristen
- Jahressperre (12 Monate) [✅ / ❌]
- 15-Monats-Frist [✅ / ❌] Wirksam ab: <Datum>
- Überlegungsfrist Ende <Datum>
- Klagefrist Vermieter Ende <Datum>
V. Ortsübliche Vergleichsmiete Mietspiegelwert: <Wert>
Forderung: <Wert> [innerhalb / darüber]
VI. Kappungsgrenze (§ 558 Abs. 3) Ausgang + <20 % / 15 %> = <Wert>
Forderung: <Wert> [✅ / überschießend <Differenz>]
VII. Abgrenzung § 559 BGB [N/A / Verdacht — gesondert prüfen]
VIII. Mietpreisbremse (§§ 556d ff.) [N/A / Ausgangsmiete gerügt]
IX. Zulässiger Erhöhungsbetrag <Min(Vergleichsmiete, Kappungsgrenze)>
Empfehlung [versandfertig / nachbessern] bzw.
[Zustimmung voll / teilweise <Wert> / verweigern]
Ergebnis: <wirksam / teilweise wirksam / unwirksam>
Risiko Zustimmungsklage: [🟢 / 🟡 / 🔴]
Risks / typical mistakes
- Form confused with amount — a request that is invalid as to form is invalid as a whole; the amount then no longer needs to be examined at all.
- Annual blocking period and 15-month period conflated — one concerns receipt, the other validity; a premature request is invalid and costs a full new waiting period.
- Means of substantiation too unspecific — a blanket reference to "the rent index" without classifying the apartment, or comparable apartments without a findable address, are not sufficient.
- Capping limit calculated incorrectly — three-year period set incorrectly, cumulative prior increases forgotten, or the lowered 15% limit overlooked.
- Rent index not current — without adjustment after two years (§ 558d(2) BGB), the presumption effect of the qualified rent index lapses.
- Request addressed to only one of several tenants or without presentation of authority (§ 174 BGB) → invalid or rejectable.
- Modernization disguised as a comparative rent increase — § 559 BGB follows its own rules; mixing them must be objected to.
- Partial consent missed — where the request is only partly well-founded, consent in the valid amount was omitted and thereby an unnecessary litigation risk was created.
- Deadline for action under § 558b(2) sentence 2 BGB missed — the entire request must be redrafted.