First, a fact. BIK is not a blacklist. It's a register of credit behaviour, positive and negative. Paying on time builds a history. No history is almost as bad as a bad history, because the bank has nothing to score you against.
What actually moves the score
On-time payments. Roughly 35% of the model. A 30-day delay weighs on you for years. Paying on the 15th when the due date was the 1st doesn't help anyone.
Not maxing out a credit line. If a card has a 20 000 PLN limit and you constantly carry an 18 000 PLN balance, the system reads it as financial stress. Keep utilisation under 30% of the limit, at least on the statement date, because that's when it gets reported to BIK.
Account age. A five-year-old card with a clean history weighs more than three new cards. Don't close old cards on autopilot.
What people think helps but doesn't
Taking out several small loans „for the history" in the same quarter. Each application counts as an enquiry and pushes the score down. Two products a year is the cap if you're building a track record.
Paying off and immediately closing the account. Account age counts as long as the account stays open and is serviced without late payments. Closing it can actually drop the score.
How to check your report
Order a BIK report at bik.pl — the basic version costs a few dozen zloty. Look for: identity errors, accounts you no longer have that are still showing as open, or late payments wrongly reported. These are more common than people think. A complaint takes 4–6 weeks and is worth filing.