The technical gap between WIBOR and WIRON is fundamental. WIBOR is an average of bank quotes for 1, 3, 6 or 12-month loans. WIRON is the average of actual overnight transactions from the previous day. WIRON is backward-looking from transactions, WIBOR forward-looking from quotes. Because overnight transactions cost less than longer quotes, WIRON usually sits 0.3–0.7 pp below WIBOR at the same moment.
A WIRON mortgage in practice. Usually WIRON 3M (a weighted average of daily WIRON over the last 3 months) plus the bank margin. The payment resets every 3 months, same as WIBOR 3M. For the client the visible difference is usually a payment lower by 100–200 PLN on a 400 000 PLN mortgage compared to the same loan on WIBOR. But you have to compare the full package: a bank offering WIRON may quote a higher margin (say, 2.6% instead of 2.3%) — total effect is the sum.
Migration of existing WIBOR mortgages to WIRON is under way and ends in 2027. The bank sends a contract annex with the new benchmark and a small margin tweak (a few basis points to balance the WIBOR–WIRON gap at the switch moment). The borrower can refuse — the loan stays on old WIBOR — but KNF has said WIBOR publication ends after 2028, so refusal only defers the decision.
Frequently asked questions
Around 3.9% in June 2026. Systematically 0.3–0.7 pp below WIBOR 3M. Check the live figure on gpwbenchmark.pl.
Yes, the annex needs your consent. But KNF has scheduled WIBOR publication to end by 2028, so refusal only postpones a mandatory migration.
In practice yes. New mortgages since 2025 must ride on WIRON. Some banks still offer WIBOR on request, but that is fringe.