DSTI (debt service to income)
DSTIDSTI (debt service to income) is the share of net income that goes on loan payments; since 1 July 2023 it is a bank rule, not a ČNB limit. The ČNB deactivated it on that date and has not set one since. Banks still calculate DSTI under their own internal rules, usually with a threshold of 40–50 %: 45 % as standard and 50 % for applicants under 36.
Example
Net income is CZK 60,000, a consumer loan costs CZK 3,000 a month and a CZK 4,000,000 mortgage over 30 years at 5.00 % adds a payment of CZK 21,473. Payments total CZK 24,473, which puts DSTI at 40.8 %. A bank with an internal threshold of 45 % will approve the loan; one with 40 % would want the consumer loan paid off first.
In practice
Banks also count payments that do not exist yet, usually a portion of your credit card and overdraft limits. With co-applicants, both incomes and both sets of payments are added up. Some banks stress-test with a higher rate than the one they offer, so their DSTI comes out worse than in your own spreadsheet. Treating one bank's threshold as the rule is a mistake, since another may allow 5 pp more.
How it differs
DTI measures total debt against annual income; DSTI measures the monthly burden of repayments. For the same debt, a longer term or a lower rate improves DSTI but leaves DTI unchanged. LTV has nothing to do with income: it compares the loan with the property's value, and the ČNB sets its 80 % limit as mandatory.
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