Indexmiete: How to Calculate a VPI Increase (2026)

What is an Indexmiete? (in plain terms)

An Indexmiete (index-linked rent) is a rent that tracks the Verbraucherpreisindex (VPI, the consumer price index) of the Statistisches Bundesamt (Federal Statistical Office). The key consequence for you as a landlord: you do not have to justify a Vergleichsmiete (comparable local rent) or cite a Mietspiegel (the official local rent index) — the permitted increase follows the VPI alone.

The central rule: the new rent rises by the same percentage as the VPI between two reference dates, but the rent must have stayed unchanged for at least one year, and you must declare the increase in Textform (text form, e.g. a letter or email) stating the index change (§ 557b BGB).

The formula: how to calculate the new Indexmiete (§ 557b Abs. 1 BGB)

The relevant figure is the Verbraucherpreisindex für Deutschland of the Statistisches Bundesamt, current base year 2020 = 100 (§ 557b Abs. 1 BGB).

The formula is:

new rent = old rent × (new VPI / old VPI)

Or as a percentage increase:

[(new VPI / old VPI) × 100] − 100 = percentage change

Worked example: Your starting rent is 800 EUR (agreed on the basis of VPI 109.8). The current VPI (April 2026) stands at 125.2.

• 800 EUR × (125.2 / 109.8) = 912.20 EUR
• Increase: (125.2 / 109.8 − 1) × 100 = +14.0 %

So the new Nettokaltmiete (net cold rent) is 912.20 EUR. Betriebskosten (operating costs) and heating are unaffected by the index adjustment — the Indexmiete applies only to the Nettokaltmiete.

Achtung: Always apply the index against the same base figure used in the Mietvertrag (lease) or in the last adjustment. Using an outdated index series (e.g. base year 2015) or picking the starting value freely risks an invalid increase. The current series of the Statistisches Bundesamt (base 2020 = 100) is what counts.

The lock period: at least one year (§ 557b Abs. 2 BGB)

Between two index adjustments the rent must stay unchanged for at least one year (§ 557b Abs. 2 BGB). The period starts with the last rent change — for the first increase that means from the start of the tenancy, and after that from each most recent adjustment.

During an Indexmiete an increase under § 558 BGB (Vergleichsmiete) is expressly excluded (§ 557b Abs. 2 BGB). Alongside the index adjustment, only increases for structural measures beyond your control and adjustments to Betriebskosten under § 560 BGB remain possible.

Form and timing of the declaration (§ 557b Abs. 3 BGB)

The increase is asserted by a declaration in Textform (§ 557b Abs. 3 BGB). A letter or an email is enough; a handwritten signature is not strictly required.

The declaration must state:

• the change in the price index that has occurred (old and new VPI level),
• the respective rent or the increase as a monetary amount.

The changed rent is payable from the start of the second month after the declaration is received (§ 557b Abs. 3 BGB). If the declaration arrives in March, the tenant owes the new rent from 1 May. A retroactive increase is not possible.

Step by step

1. Determine the index levels — old VPI (from the Mietvertrag or last adjustment) and current VPI (Statistisches Bundesamt, base 2020 = 100).
2. Check the lock period — has at least one year passed since the last rent change (§ 557b Abs. 2 BGB)?
3. Calculate the new rent — old rent × (new VPI / old VPI).
4. Draft the declaration in Textform — with the old and new VPI level and the concrete increase amount (§ 557b Abs. 3 BGB).
5. Set the due date — from the start of the second month after receipt.

Indexmiete vs. increase by Mietspiegel

Feature	Indexmiete (§ 557b BGB)	Vergleichsmiete (§ 558 BGB)
Basis	VPI of the Statistisches Bundesamt	Mietspiegel / comparable flats
Kappungsgrenze	does not apply	20 %, 15 % in tight markets, over 3 years
Mietspiegel	irrelevant	decisive
Frequency	earliest after 1 year	earliest 15 months, lock + waiting period
Form	Textform with index figure	Textform with justification
Tenant consent	not required	required (§ 558b BGB)

Common mistakes

• Wrong base figure. Taking the old VPI from an outdated index series (e.g. base 2015) instead of the current series (base 2020 = 100).
• Lock period ignored. Increasing before one year has passed since the last adjustment (§ 557b Abs. 2 BGB).
• Index figure missing. The declaration states only the new rent, not the change in the price index (§ 557b Abs. 3 BGB) — which makes it invalid.
• Wrong due date. Demanding the new rent from the next month rather than the second month after receipt.
• Applying the Kappungsgrenze. Artificially limiting the increase even though the Kappungsgrenze does not apply to an Indexmiete.
• One-sided clause. An index clause that permits only increases and excludes decreases can be invalid in full — an Indexmiete follows the VPI in both directions.

HausMaus makes this easier

HausMaus produces the Indexmiete increase as a finished document: you enter the old and the current VPI, HausMaus computes the new rent under § 557b Abs. 1 BGB and drafts the increase declaration in correct Textform — stating the index change and the increase amount, exactly as § 557b Abs. 3 BGB requires. The one-year lock period and the due date from the second month onwards are taken into account, and the document can be reviewed before sending and filed in the digital Mietakte (rental file). Wohnen, geregelt. (Home, handled.)