In Polish: WIRON
This is the word you will see in bank documents.
Definition
WIRON (Warsaw Interest Rate Overnight) is an overnight rate index that, in the first version of the reform, was meant to replace WIBOR in loans. At the end of 2024 the working group on the benchmark reform dropped this choice and selected POLSTR instead. Today, when someone talks about a WIRON mortgage, they usually mean POLSTR.
What it means for you
In a new variable-rate mortgage agreement you will see POLSTR or, until the end of 2026, WIBOR, not WIRON. If you read older articles or calculations based on WIRON, treat them as a description of the mechanism, not a current offer. Formally, WIRON and POLSTR are two different indices with their own methodology.
Full entry in Polish, with a worked example and sources
Frequently asked questions
Are WIRON and POLSTR the same thing?
No. WIRON was an earlier candidate to succeed WIBOR, dropped at the end of 2024. POLSTR was chosen instead and has been calculated by GPW Benchmark since June 2025.
Can I get a mortgage based on WIRON?
New variable-rate loans are based on POLSTR or, until the end of 2026, on WIBOR. If a bank uses the name WIRON in its materials, ask which benchmark exactly will be in the agreement.
Related terms
Definitions are simplified and reflect Polish law and bank practice as of October 2026. Where every word matters, the Act and your loan agreement decide. Figures in examples are indicative and are not a bank offer. The Polish version of each entry has worked examples and sources.
Other terms in “Interest rates and benchmarks”