Index rent calculator: is the new rent worked out correctly?
Pick the two index values from your landlord’s letter; the calculator checks the new rent and the date it applies from.
Checked by Radif Partners · Editorial policy · Method
New rent under the index
€925.76
+2.86 % · +€25.76 per month
| Old CPI | 122.3 |
| New CPI | 125.8 |
| Payable from | 1 December 2026 |
The rent must stay unchanged for at least a year between two adjustments. The written notice states both index values and the new rent or the increase in euros (Section 557b(3) BGB).
How we calculateWith an index-linked rent (Indexmiete) the net cold rent moves in line with Germany's consumer price index, which the Federal Statistical Office (Destatis) publishes every month (Section 557b of the Civil Code). The calculation uses the index at the last adjustment and the new index: new rent equals old rent times the new value divided by the old value. At least a year must pass between two adjustments, and the new rent is only payable from the start of the month after next once the notice has reached you. The calculator holds every monthly value on the 2020 = 100 base from January 2021 to August 2026. Example: rent of €900, index 122.3 in August 2025 and 125.8 in August 2026. That is a rise of 2.86 %, so the new rent is €925.76. If the notice arrives on 15 October 2026, it applies from 1 December 2026. If the index falls, the tenant may ask for a reduction.
How the calculator works
It takes the index for the month the rent was last adjusted or agreed, and the index the landlord now relies on, both from the Federal Statistical Office table. The new rent is the old rent times the ratio of the two values, rounded to the cent. The date it becomes payable follows from Section 557b(3) BGB: the start of the month after next once the notice has arrived. Whether a year has passed since the last adjustment you can check against the date of the last change; modernisation increases and service-charge changes do not count.
The latest index values
| Month | CPI 2020 = 100 | Change on the same month a year earlier |
|---|---|---|
| August 2026 | 125.8 | 2.9 % |
| July 2026 | 125.6 | 2.8 % |
| June 2026 | 124.6 | 2.3 % |
| May 2026 | 125.0 | 2.6 % |
| April 2026 | 125.2 | 2.9 % |
| March 2026 | 124.5 | 2.7 % |
With an index-linked rent, an increase up to the reference rent is ruled out, and a modernisation increase is only possible in narrow cases. The rent brake applies only to the starting rent. More on the index-linked rent page; the comparison with fixed steps is on the graduated rent page.