How to Hold and Invest a Mietkaution (2026)
Updated 6/14/2026 · HausMaus Redaktion
The Mietkaution (rental deposit) may not exceed three Nettokaltmieten (net cold rents) (§ 551 Abs. 1 BGB). The landlord must hold it separately from their own assets, insolvency-proof and interest-bearing – typically at the rate for savings with three months' notice (§ 551 Abs. 3 BGB). The accrued interest belongs to the tenant. The tenant may pay in three equal monthly instalments.
What does it mean to "hold and invest a Mietkaution"?
The Mietkaution (rental deposit, also Mietsicherheit – tenancy security) is security the tenant provides at the start of the tenancy. The landlord may not treat it as their own money: it must be held separately from their personal assets, insolvency-proof and interest-bearing, and returned at the end with the interest (§ 551 Abs. 3 BGB). This guide covers holding and investing the Kaution during the tenancy – not deductions at move-out (for that: Kaution einbehalten).
Amount and instalments (§ 551 Abs. 1 und 2 BGB)
Two limits apply from the start:
- Maximum: at most three times the Nettokaltmiete (net cold rent) – the rent without operating costs shown as a flat rate or prepayment (§ 551 Abs. 1 BGB). Anything agreed above that is void.
- Instalments: the tenant may pay in three equal monthly instalments (§ 551 Abs. 2 BGB). The first is due at the start of the tenancy, the rest with the next two rents. A clause excluding this is void.
The investment duty: separate, insolvency-proof, interest-bearing (§ 551 Abs. 3 BGB)
This is the landlord's central duty for a cash deposit:
- Getrennte Anlage (separate investment): the deposit must be held separately from the landlord's assets – not on their private account, but recognisably as trust money.
- Insolvenzfest (insolvency-proof): because it is kept separate, the deposit is beyond the reach of creditors if the landlord becomes insolvent and stays with the tenant.
- Interest-bearing: it must earn at least the rate usual for savings with three months' notice. Any bank within the EU is permitted.
- Interest belongs to the tenant: the accrued interest increases the security and is paid out at the end of the tenancy (§ 551 Abs. 3 Satz 3 BGB). Exception: student and youth hostels.
Achtung (caution): Mixing the Kaution with your personal assets breaches § 551 Abs. 3 BGB. The tenant then has a claim to demonstrably separate, insolvency-proof investment – and may withhold ongoing rent up to the amount of the deposit until you prove correct investment (BGH, VIII ZR 234/13).
What forms of Mietsicherheit are there?
A deposit need not be cash on an account. Three forms are common:
| Form | How it works | Who pays / holds |
|---|---|---|
| Kautionskonto / Kautionssparbuch | Landlord invests the cash deposit separately and interest-bearing (§ 551 Abs. 3 BGB) | Tenant pays in; landlord holds it insolvency-proof |
| Verpfändetes Sparbuch (pledged savings) | Tenant opens their own account and pledges it to the landlord | Tenant is account holder; interest accrues to them |
| Mietkautionsbürgschaft / -versicherung (deposit guarantee/insurance) | A bank or insurer guarantees the deposit amount | Tenant pays an annual premium; no savings balance |
With a cash deposit, the full investment duty falls on the landlord. With a pledged Sparbuch, the tenant is the account holder, so the interest accrues to them anyway. A Bürgschaft (guarantee) ties up no balance – there is no interest, but an ongoing premium borne by the tenant.
Step by step: holding the deposit correctly
- Check the amount – at most three Nettokaltmieten (§ 551 Abs. 1 BGB).
- Agree the form – cash deposit, pledged Sparbuch, or Bürgschaft.
- For a cash deposit: open a separate account – a recognisable trust / Kautionskonto, separate from your personal assets.
- Invest interest-bearing – at least the usual savings rate.
- Allow instalments – three equal monthly instalments if the tenant asks.
- Document it – record the amount, where it is held and the interest accrued, so move-out can be settled quickly and correctly.
Common mistakes
- "Parking" the deposit on your own private account.
- Demanding more than three Nettokaltmieten.
- Excluding instalment payment in the contract.
- No interest, or too little – the interest belongs to the tenant.
- Not documenting where it is held and the interest accrued, leaving the move-out settlement unclear.
Mit HausMaus geht das einfacher
HausMaus tracks the Kaution for each tenancy: you record the amount, the chosen instalments, and where the deposit is held (with the landlord, on a Kautionskonto, or with a provider). When the deposit is held by the landlord directly, HausMaus points to a separate, insolvency-proof account under § 551 BGB. Everything is documented and ready for the interest-bearing return at move-out.
Frequently asked questions
How high can the Mietkaution be?
At most three times the Nettokaltmiete (net cold rent) – the rent without operating costs shown as a flat rate or prepayment (§ 551 Abs. 1 BGB). Any agreement above that is void to the excess, and the tenant can reclaim the surplus.
Where must the landlord hold the deposit?
Separately from their own assets, insolvency-proof and interest-bearing – typically on a Mietkautionskonto (dedicated deposit account) or Kautionssparbuch (deposit passbook) at a bank, at the rate usual for savings with three months' notice (§ 551 Abs. 3 BGB). Any bank within the EU is permitted.
Who owns the interest on the Mietkaution?
The tenant. The interest increases the security and is paid out with the deposit at the end of the tenancy (§ 551 Abs. 3 Satz 3 BGB). The landlord may not keep it. Exception: student and youth hostels (§ 551 Abs. 3 Satz 5 BGB).
Can the tenant pay the deposit in instalments?
Yes. The tenant may pay a cash deposit in three equal monthly instalments (§ 551 Abs. 2 BGB). The first is due at the start of the tenancy, the others with the next two rent payments. The contract cannot remove this right.
What happens if the landlord does not hold the deposit separately?
If the landlord fails to hold the deposit separately and insolvency-proof, the tenant may withhold rent up to the amount of the deposit until correct, separate investment is proven (BGH, VIII ZR 234/13). Mixing it with personal assets also gives the tenant a claim to proper, separate investment.
Sources
This guide is based on the statute text and official sources. You can read the cited paragraphs in the original here: