Full definition
Bank margin is one of the two components of variable mortgage interest (the other is WIBOR or WIRON). The margin is negotiated and fixed at contract signing, and — subject to very narrow exceptions — stays constant for the entire repayment period, unlike WIBOR which fluctuates. In 2026, mortgage margins for PLN loans range from roughly 1.7% to 2.5%. The margin depends on: down payment (higher deposit = lower margin), BIK score, loan size, cross-sell products (current account, card, insurance), existing relationship with the bank. A 0.5 p.p. difference (2.0% vs 2.5%) on a 400,000 PLN / 25-year mortgage costs roughly 130 PLN per month and ~39,000 PLN over the full term — which is why margin is one of the most important items to negotiate.
Concrete numeric example
Offer: WIBOR 3M + 2.2% margin = 7.49% interest. Ten years later, if WIBOR falls to 3.5%, the total rate becomes 5.7%. With a 2.5% margin the rate would stay 0.3 p.p. higher for the full term, regardless of WIBOR moves.