Question 1

How do I calculate the new index rent?

Accepted Answer

The rent changes in the same proportion as the consumer price index: new rent = current rent × new index ÷ old index. Example: €800 net rent, index rose from 110.0 to 115.5. 115.5 ÷ 110.0 = 1.05, so the new rent is €840. What matters is the percentage change, not the difference in index points. The calculator above fills in the official monthly values automatically.

Question 2

From when do I have to pay the increased index rent?

Accepted Answer

From the start of the month after next following receipt of the declaration (§ 557b(3) BGB). If the letter arrives on 24 September, the new rent applies from 1 November. In addition, the rent must have remained unchanged for at least one year since the last change (§ 557b(2) BGB). The later of the two dates applies. There is no retroactive increase.

Question 3

Is there a cap (Kappungsgrenze) on index rent?

Accepted Answer

No. The cap of 20% or 15% within three years is in § 558(3) BGB and only applies to increases up to the local comparative rent. Such increases are excluded during an index rent (§ 557b(2) BGB). An index rent therefore follows the consumer price index alone, even when inflation is high, as in 2022 and 2023. The only outer limit is the rule against excessive rents (§ 5 of the Economic Offences Act, WiStG).

Question 4

What form must an index rent increase take?

Accepted Answer

Text form under § 126b BGB: a letter, email or fax that shows who is making the declaration. No signature is required. The letter must state the change in the price index and the new rent or the increase in euros. The increase does not happen automatically. As long as the landlord makes no declaration, the current rent remains.

Question 5

Can the index rent also go down?

Accepted Answer

Yes. The index rent is determined by the index, in both directions. If the consumer price index falls compared with the level at the last adjustment, tenants can demand a reduction by a declaration in text form. The one-year rule and the "month after next following receipt" date also apply then. In practice this is rare, because the index has risen almost continuously since 2015.

Question 6

Which index months must the landlord use?

Accepted Answer

The law does not prescribe specific months. Common practice compares the index level at the time of the last adjustment (or start of the lease) with the latest value published before the declaration. Some leases name fixed months. Important: both values must use the same base, currently 2020 = 100. If the landlord takes the old level from a month before the last adjustment, the increase comes out too high, because part of the rise is counted twice.

Question 7

Does the rent brake apply to an index rent?

Accepted Answer

Only for the initial rent (§ 557b(4) BGB). In areas with a rent brake, the rent at the start of the lease may be at most 10% above the local comparative rent, with exceptions such as a higher previous rent. Later index increases are no longer measured against the rent brake. Graduated rent is different: there the rent brake applies to every step.

Question 8

Can the landlord also increase the rent for modernisation under an index rent?

Accepted Answer

Only to a limited extent. Under § 557b(2) BGB, a modernisation increase (§ 559 or § 559e BGB) is only possible insofar as the landlord carried out the building work due to circumstances beyond their control, such as legal obligations. Exception: modernisations under § 555b no. 1a BGB (heating system). Service charges are adjusted separately under § 560 BGB.

Guide: Index Rent Calculator

Index Rent in Germany 2026: Formula, Deadlines and Your Rights

Checking an Index Rent Increase: The 6 Key Points

Index Rent or Graduated Rent? A Comparison for Tenants and Landlords

Index Rent and the Rent Brake: What Applies to the Initial Rent

The Consumer Price Index Explained: Base Year, Monthly Values, Rebasing

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