On September 3, 2026, something that had been announced for years as a distant reform quietly became a real offer at a bank branch. PKO Bank Polski and PKO Bank Hipoteczny became the first institutions in Poland to sell new mortgage loans based on the POLSTR benchmark rather than the decades-old WIBOR. This is the first genuine, commercial step in the long-running process of phasing out WIBOR — and a good moment to explain what it actually means for the wallets of people currently shopping for a mortgage, and for those already repaying one.
What POLSTR is, and why it exists at all
POLSTR (Polish Short Term Rate) is a reference rate administered by GPW Benchmark, officially in force since September 2025. The key difference from WIBOR lies in how it is calculated: POLSTR is based exclusively on actual overnight interbank deposit transactions, rather than — as WIBOR sometimes was during periods of low market liquidity — partly on expert declarations from panel banks about what rate they believed was appropriate. It is the same direction of reform that, after the LIBOR scandal, the EU's BMR regulation forced across Europe: benchmarks should reflect what actually happens in the market, not what banks say might happen.
The timeline for phasing out WIBOR is already fixed and irreversible. The overnight rate (WIBOR O/N) stops being calculated from October 1, 2026, and WIBOR 1Y from December 21, 2026. The most commonly used rates in mortgage contracts — WIBOR 1M, 3M and 6M — will still be published until December 31, 2036, but only to service existing contracts. No new loans will be issued referencing WIBOR once the transition period ends.
What exactly changed at PKO BP from September 3
According to PKO Bank Hipoteczny's announcement, from September 3 to October 2, 2026, information forms and pricing proposals for its Digital Mortgage product are now calculated using the POLSTR 1M compounded rate rather than the previous WIBOR 3M. In the representative example published by the bank, the variable interest rate is 5.66373% — the sum of the POLSTR 1M compounded rate of 3.55373% and a bank margin of 2.11 percentage points. The APRC in that example is 6.39%.
An important caveat that several press reports gloss over: switching the reference benchmark does not automatically make a mortgage cheaper. POLSTR and WIBOR are simply two different methodologies for measuring essentially the same underlying interbank cost of money, and the final cost of a loan still depends primarily on the level of NBP interest rates and the margin a bank adds — not on which label the benchmark carries. Anyone expecting the switch to POLSTR itself to lower their instalment will be disappointed.
What this means for current and future borrowers
For people already repaying a WIBOR-based mortgage, nothing changes for now. The switch applies only to new sales — contracts signed before September 3 remain on their existing terms, and any future conversion mechanism to POLSTR will be established separately, likely as part of the nationwide roadmap for the reference-rate reform. There is no need to call your bank asking whether you need to sign anything — at this point, you do not.
For people who are still shopping for a mortgage, the situation is different and requires a bit more care when comparing offers. A few practical pointers:
- Compare the APRC, not just the benchmark's name. The APRC bundles all the costs of a loan and lets you realistically compare a POLSTR-based offer against one still built on WIBOR at another bank.
- Check the size of the margin. It is the bank's margin, not the reference benchmark itself, that is negotiable and that genuinely differs between lenders.
- Consider a fixed rate for the first few years. Banks, including PKO BP, currently offer an alternative fixed rate locked in for five years, unaffected by POLSTR fluctuations — worth considering while the new benchmark is still settling in on the market and its behaviour is harder to forecast than the long-familiar WIBOR.
- Don't assume in advance which option will be cheaper. That depends on the future path of NBP interest rates, which nobody can know ahead of time — so base the decision on your own risk tolerance, not on market trends.
Why this matters even if you don't have a mortgage
The WIBOR-to-POLSTR reform is not limited to home loans. Eventually the new benchmark will also underpin the interest rates of some cash loans and business products, so it's worth getting familiar with it now, before it becomes the market standard. Anyone planning to take on any variable-rate obligation in the coming months should treat POLSTR's arrival as a signal to read every offer presented to them more carefully than usual.
What you should do
If you already have a WIBOR-based mortgage, there is nothing to do right now except watch for your bank's future communications about conversion. If you're still looking for financing, don't be guided by the benchmark's name alone — focus on the real APRC and the margin in each specific proposal. Before signing anything, it pays to line up several offers side by side — compare current mortgage offers and see how POLSTR-based pricing stacks up against still-available WIBOR-based deals. If you're also financing something else, take the chance to check the personal loan rankings too — the same rules for comparing APRC and margin apply there just as well.