Indexmiete: calculating a VPI increase correctly
How to work out the new rent for an Indexmiete (index-linked rent) from the consumer price index (VPI), and how to ask for the increase so that it is valid.
The formula is: new rent = old rent × (new VPI ÷ old VPI). Ask for the increase by letter or email, no sooner than one year after the last change, and state the change in the index.
What an Indexmiete increase needs
The calculation is simple. But the increase only takes effect if your notice contains the right details.
- 1
Use the formula
New rent = old rent × (new VPI ÷ old VPI). The VPI is the consumer price index of the Statistisches Bundesamt (Federal Statistical Office).
- 2
Use the same index series
Take both index figures from the same, current series.
- 3
Wait one year between increases
The rent must stay the same for at least one year between two changes.
- 4
Ask in text form
Ask for the increase by letter or email. Saying it aloud is not enough.
- 5
State the index change
Give the old and new index figure and the new amount. Otherwise the notice is invalid.
- 6
When the new rent starts
The new rent is due from the start of the second month after the notice arrives. The tenant does not have to agree.
Why this matters
Under § 557b Abs. 3 BGB, you must tell the tenant about the rent change in text form. You must state the change in the index and the new rent or the increase in euros. If you leave that out, the tenant does not owe the higher rent.
General information, not legal advice.
Frequently asked questions
How do I calculate an Indexmiete increase?
Use the formula new rent = old rent × (new VPI ÷ old VPI), with base year 2020 = 100. Example: a rent of €800 with an old VPI of 109.8 and a new VPI of 125.2 gives 800 × (125.2 ÷ 109.8) = €912.20.
Does the tenant have to agree to an Indexmiete increase?
No, the tenant does not have to agree. The new rent is due from the start of the second month after your notice arrives. But the notice must be in text form and state the change in the index. Otherwise it is invalid.
Does the Mietpreisbremse apply to an Indexmiete?
The Mietpreisbremse (rent brake) only applies to the starting rent when the lease begins (§ 557b Abs. 4 BGB). It does not limit the later changes that follow the index.
Also in this topic: Mietpreisbremse 2026: how much can the new rent be?Rent increase after modernisation: pass on 8%Passing the Grundsteuer on to tenants: 2026 guide
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