Penalty interest kicks in only when you miss the instalment date. The bank does not usually charge it in the first few days directly — a reminder SMS or a phone call goes out first. Formally, though, the clock starts on day one after the due date. It runs on the overdue amount, not the whole loan. Example: 800 PLN instalment, 30 days late, penalty rate 20% a year — about 13 PLN in interest. The reminder fee (30–50 PLN) usually hurts more than the penalty interest itself.
One important distinction: penalty interest is not the same as collection costs. The bank can charge penalty interest automatically up to the statutory ceiling, but collection fees have to be written into the contract and are capped there. A lender adding 200 PLN for a „collection phone call" with no contractual basis is breaking the law — you have grounds for a complaint and a UOKiK filing.
If the delay drags on, the bank usually terminates the contract after 90 days. From that point penalty interest runs on the whole remaining balance, not just the overdue instalment. This shift blows up the cost, so at the first signs of trouble it is better to call the bank and renegotiate the schedule than to keep quiet.
Frequently asked questions
The civil code (art. 481 §2¹) caps it at 2 × NBP reference rate + 5.5 pp — around 20% a year in 2026. The contract may set a lower rate.
Yes, from day one after the missed instalment. Termination is not a precondition, just the next step if the delay drags on.
Pay the overdue amount as soon as you can. Penalty interest is calculated daily, so every day matters. For longer trouble: a rescheduling annex.