Full definition
DSTI (Debt Service-to-Income) is the central metric in KNF's Recommendation S for creditworthiness assessment. It shows what share of monthly net income is absorbed by all financial obligations: loan instalments, alimony, credit card (30% of granted limit), the planned new instalment. KNF recommends DSTI ≤ 40% for income below 6× minimum wage (~26,000 PLN in 2026) and ≤ 50% above. Banks apply internal limits — some up to 60%, others cap at 35%. DSTI rises when you take new debt, raise credit-card limits, or add a new obligation. It falls when you repay existing loans, cancel cards, or income grows.
Formula
DSTI = (Σ monthly instalments + alimony + 30% × card limits) / net income
Concrete numeric example
Net income 8,000 PLN, current loan instalment 800 PLN, credit-card limit 10,000 PLN (30% = 3,000 PLN service in the bank model). Planned loan: 2,400 PLN instalment. DSTI = (800 + 50 + 2,400) / 8,000 = 41%. Exceeds the 40% ceiling — the bank will likely reduce the amount or refuse.