An index-linked rent (Indexmiete) ties the rent on a residential lease to the German consumer price index (Verbraucherpreisindex, VPI) published by the Federal Statistical Office (Destatis). It is governed by section 557b of the German Civil Code (BGB). Instead of arguing over the local comparative rent, the rent moves with measured inflation: when the VPI rises, the landlord may raise the rent by the same percentage. This guide gives you the formula, a worked example, the formal notice requirements, and the mistakes that most often make an increase void.
The Indexmiete formula
The adjustment is a simple proportion. The new rent equals the old rent multiplied by the new index value and divided by the old index value:
new rent = old rent x (new VPI / old VPI)
The old VPI is the index value at the start of the lease or at the date of the last adjustment. The new VPI is the current value. Because the rent rises by exactly the percentage change in the index, you can also read the increase as old rent x ((new VPI / old VPI) - 1). Always use the official all-Germany VPI (base year 2020 = 100), never a regional series, and make sure both values sit on the same base year. When Destatis rebases the index, use its linked back-series so the two values stay comparable. The index applies only to the net cold rent (Nettokaltmiete); the operating cost prepayment is left untouched.
A worked example
Assume a net cold rent of 850 EUR, an old index of 116.0, and a new index of 122.0.
| Item | Value |
|---|---|
| Old net cold rent | 850.00 EUR |
| Old VPI (base 2020 = 100) | 116.0 |
| New VPI | 122.0 |
| Index factor (122.0 / 116.0) | 1.0517 |
| New net cold rent (850 x 122 / 116) | 893.97 EUR |
| Monthly increase | 43.97 EUR |
| Percentage increase | 5.17% |
The rent rises by 5.17 percent, the same as the index. If the tenant also pays an operating cost prepayment, that figure is not affected by the index calculation.
Formal requirements under section 557b BGB
Getting the arithmetic right is not enough; the increase only takes effect if you follow the procedure:
- Written clause. The Indexmiete agreement must be made in writing in the lease itself. Without a valid clause there is no index rent.
- Twelve months unchanged. Apart from modernization (section 559) and operating cost changes (section 560), the rent must remain unchanged for at least one year. A new index adjustment can therefore take effect at the earliest twelve months after the last rent change.
- Text-form notice. The increase is asserted by a declaration in text form (section 126b BGB); a letter or an email is enough, a handwritten signature is not required. Standard practice is to state the old and new index values and the percentage, but the law specifically requires you to give the new rent or the increase as a euro amount (Geldbetrag). A percentage alone is not sufficient.
- Effective from the month after next. The changed rent is due from the beginning of the second month after the tenant receives the notice. If the notice arrives in March, the new rent is owed from 1 May. It is never retroactive.
- No parallel comparative-rent increase. During an index rent you cannot also raise the rent to the local comparative rent under section 558. Only a modernization you did not cause and operating cost changes run alongside the index.
Common mistakes
- Raising the rent more often than once every twelve months.
- Stating only a percentage and leaving out the new rent or the increase as a euro amount.
- Charging the new rent from the following month instead of the month after next.
- Mixing index values from different base years without using the linked series.
- Applying the factor to the gross (warm) rent instead of the net cold rent.
- Stacking a section 558 comparative-rent increase on top of the index in the same period.
- Losing the paper trail. Commercial landlords must retain the notice and the index proof under GoBD and HGB rules (invoices eight years, business correspondence six).
Where REPM stores the index clause
REPM keeps the lease and its index clause on the property record, alongside units, tenants and maintenance in the property management module. Each lease stores the base index, the base date, the current net cold rent and the date of the last adjustment, so the twelve-month rule and the correct old VPI are always at hand. When Destatis publishes a new value you apply the formula, generate the text-form notice, and archive it with the calculation, which is exactly the paper trail the GoBD retention rules expect. Operating cost prepayments, which the index never touches, live in the same lease and feed your Nebenkostenabrechnung. You can start a free REPM Lite trial and set up your first index lease in minutes.
Frequently asked questions
Can I combine an index-linked rent with a step-up rent?
No. An index-linked rent (section 557b) and a step-up rent (Staffelmiete, section 557a) are mutually exclusive for the same period. In the lease you agree one or the other, not both.
Which index value do I use?
The official all-Germany consumer price index (VPI) from Destatis, base year 2020 = 100. Use the value for the relevant month and keep the old and new values on the same base year.
Does the Mietpreisbremse cap an index increase?
The Mietpreisbremse limits the initial rent at the start of the lease. Later index adjustments follow the VPI and are generally not capped by it, provided the starting rent was lawful.
How soon can I raise the rent again?
At the earliest twelve months after the last rent change. The new rent is then due from the month after next, once the tenant has received your text-form notice.