Creating a Mietvertrag as a landlord (2026, §§ 535 ff. BGB)

What must a Mietvertrag contain?

A residential Mietvertrag (tenancy agreement) is the foundation of the tenancy and is governed by §§ 535 ff. BGB. To be valid, four points must be beyond doubt:

• The parties – full names and addresses of all landlords and tenants.
• The property – a precise description of the flat: address, floor, location, living area and any included rooms (cellar, parking space, garden).
• The rent – the net cold rent and the Nebenkosten (operating costs), each as an advance payment or a flat rate.
• The start date – the date the tenancy begins.

Everything else – the Kaution, notice terms, Schönheitsreparaturen, house rules – is sensible but not a condition of validity. § 535 BGB also sets the core duties: the landlord hands over the flat fit for use and keeps it in repair, the tenant pays the rent.

Fixed-term or open-ended?

The default is the open-ended contract, which can be terminated by ordinary notice only under the statutory conditions.

A fixed term (Zeitmietvertrag) is valid under § 575 BGB only if a statutory reason exists when the contract is signed and is given to the tenant in writing. The permitted reasons are exhaustive:

• Eigenbedarf (the landlord's own use),
• planned renovation or demolition that the tenancy would significantly hinder,
• letting to staff under a duty of service.

Without a valid reason the fixed term is invalid and the contract counts as open-ended.

Written form and § 550 BGB

A residential Mietvertrag is valid even if only oral. But if it is concluded for longer than one year, § 550 BGB requires written form. If it is missing, the contract is not void – but it counts as open-ended and can be terminated by ordinary notice after one year. In practice, therefore, every Mietvertrag should be drawn up in writing and signed by both sides.

The Kaution: at most three net cold rents

If you agree a Kaution (security deposit), its amount is capped under § 551 Abs. 1 BGB at three net cold rents – that is, rent without the Nebenkosten advance. The tenant may pay it in three equal monthly instalments, the first due at the start of the tenancy (§ 551 Abs. 2 BGB).

Important: A Kaution agreed above three net cold rents is invalid only for the excess amount – you may neither demand nor keep that part. The Kaution must also be held separately from your own assets and invested at interest.

Agreeing a Staffelmiete or Indexmiete

Future rent increases can be set out in the contract itself:

• Staffelmiete (§ 557a BGB): future rents are agreed in advance as fixed euro amounts for defined periods. Crucial: the concrete amount must be stated – a percentage alone ("rises 3 % per year") is invalid. Between two steps the rent must stay unchanged for at least one year.
• Indexmiete (§ 557b BGB): the rent follows the consumer price index of the Federal Statistical Office. Each adjustment must be requested in text form and stated as a figure.

Both models must be agreed in writing and exclude most other rent increases (such as under § 558 BGB) for their duration.

Mietpreisbremse: what caps the initial rent

In areas with a tight housing market that the relevant federal state designates by ordinance, the Mietpreisbremse (rent cap, § 556d BGB) applies. The rent on a new letting may then be at most 10 % above the ortsübliche Vergleichsmiete (local reference rent). Exceptions exist, among others, for new builds (first let after 1 October 2014) and comprehensively modernised flats. A lawful Vormiete (previous rent) may still be charged. Before signing, check whether the flat lies in a designated area.

Avoiding invalid clauses

Individual clauses can be invalid without bringing down the whole contract – the invalid clause simply drops out and the rest stays valid. This most often concerns the Schönheitsreparaturen (cosmetic repairs):

Clause	Valid?
Rigid renovation deadlines ("kitchen every 3 years, living rooms every 5")	invalid (BGH)
Shifting ongoing cosmetic repairs onto the tenant when the flat was handed over unrenovated without compensation	invalid (BGH)
Blanket end-of-tenancy renovation duty regardless of condition	mostly invalid
Flexible deadlines ("as a rule") where the flat was handed over renovated	regularly valid
Kaution above three net cold rents	invalid for the excess

Common mistakes with the Mietvertrag

• Fixed term without a statutory reason under § 575 BGB
• Kaution agreed above three net cold rents
• Staffelmiete stated only as a percentage instead of a euro amount
• Rigid Schönheitsreparaturen deadlines carried over
• Overlooking the Mietpreisbremse in a designated area
• A contract over one year without written form (§ 550 BGB)

With HausMaus it's simpler

HausMaus creates the Mietvertrag for you: you enter the parties and the flat, and the app produces a §-compliant residential tenancy agreement with the required details under §§ 535 ff. BGB – ready to review and send. The signed contract is saved automatically to your document vault, so it is on hand the moment you need it for a Nebenkostenabrechnung, a Mieterhöhung or a Kündigung.