Index rent calculator for commercial leases
New rent under an index clause in seconds: threshold, cap, floor and pass-through share — with a transparent calculation trail. The calculation runs on our server; your inputs are not stored. No sign-up.
Official CPI (Destatis, as of July 2026)Threshold logic per German case lawno data stored
Base month
Lease start or last rent adjustment
CPI (base 2020=100): 103,4
Adjustment month
CPI (base 2020=100): 125,6
0 = no threshold (every change triggers the adjustment)
Advanced clause options (trigger, cap, floor, share)
Cap = upper bound, floor = lower bound of the adjustment. A negative floor (e.g. −1) limits a rent decrease. Share = portion of the index change passed through.
Result
CPI data source: German Federal Statistical Office (Destatis), consumer price index, base 2020=100, as of July 2026 — provided via the Deutsche Bundesbank time series; the latest monthly value may be preliminary. Non-binding calculation, without warranty — no liability for the results. Your clause wording governs; not legal advice.
This index rent calculator works out the new commercial rent as “new rent = old rent × (1 + index change ÷ 100)”. The index change is (current CPI − base CPI) ÷ base CPI × 100, based on the official consumer price index of the German Federal Statistical Office (base year 2020 = 100). Many clauses only trigger an adjustment once an agreed threshold is reached (5% or 10% are common in commercial leases). The net rent is always indexed, never the gross rent — applying it to the gross rent is one of the most common mistakes. Cap (upper bound), floor (lower bound) and pass-through share can further limit the adjustment. In commercial leases, index clauses are governed by the German Price Clause Act (PrKG).
The logic behind an index adjustment
Index change
Change = (current CPI − base CPI) ÷ base CPI × 100, using the official monthly CPI values (base 2020=100).
Threshold as trigger
Once the agreed threshold (e.g. 5%) is met, the full index change is applied — not just the part above the threshold. Germany’s Federal Court of Justice ruled this expressly for residential leases (BGH, 26 May 2021 – VIII ZR 42/20); the higher regional courts apply the same reading to commercial clauses (e.g. OLG Karlsruhe, 7 Oct 2025 – 19 U 167/24). Whether “at least” or “more than” applies, and whether it is measured in percent or index points, depends on your clause.
Share, cap and floor
An agreed pass-through share is applied first; cap (upper bound) and floor (lower bound) then limit the adjustment. A negative floor caps a rent decrease.
New rent
New rent = old rent × (1 + applied change ÷ 100), rounded to cents. The net rent is indexed — applying the clause to the gross rent is one of the most common mistakes.
Deep dive with a worked example in our guide: Calculating index-linked commercial rent
Important: Germany’s Federal Court of Justice subjects standard-form commercial index clauses to unfair-terms review (11 Mar 2026 – XII ZR 51/25) — an invalid clause justifies no increase. More: Index clause invalid? Reclaiming overpaid rent
Quick answers
What is the threshold in an index clause?
The threshold defines how much the CPI must change before an adjustment is permitted — 5% or 10% are common in commercial leases. Once exceeded, the entire index change is applied, not just the part above the threshold: ruled by the Federal Court of Justice for residential leases (VIII ZR 42/20) and applied to commercial clauses by the higher regional courts (e.g. OLG Karlsruhe, 19 U 167/24). Your clause’s wording remains decisive — and its validity is a separate question.
Is “by at least 5%” the same as “by more than 5%”?
No. With “by at least 5%” a change of exactly 5.0% suffices; with “by more than 5%” it must exceed it. The calculator supports both wordings — your clause text governs.
What is the difference between percent and index points?
“By 10 points” and “by 10%” are not the same: at an index level of 125, 10 points equal only 8%. The calculator can measure the threshold in either unit.
Is the gross or the net rent indexed?
The net rent is indexed. Applying the clause to the gross rent is a common mistake that systematically inflates the result.
Can an index-linked rent also fall?
Yes — choose the “Up and down” option in the calculator so a falling CPI also lowers the rent. Whether your clause must allow a decrease (symmetry requirement) is explained in our guide on index-linked rent.
Is my input stored anywhere?
No. Your inputs are sent to our server only to run the calculation and are neither stored nor logged.
What is written in your index clause — and in the rest of your commercial lease — Boomerent makes transparent automatically: clauses, deadlines and costs at a glance (software analysis, not legal advice).