What Is the Contractual Interest Rate?
Definition
Contractual Interest Rate (Akdi Faiz): The interest rate agreed between the bank and the customer in a loan or credit card contract, before any taxes on the interest. For credit cards, a regulator may set a maximum.
The contractual interest rate (akdi faiz) is the rate agreed in a loan or credit card contract. Banks usually quote it as a monthly rate, before any taxes on the interest. On a loan it sets the interest in each installment. On a credit card it applies to the unpaid statement balance, and a regulator may set a maximum.
Where it appears in the formulas
In a loan, the monthly contractual rate is grossed up by the taxes on the interest before it enters the installment formula. On a card, one month’s interest is remaining balance × monthly contractual rate. The loan and credit card calculators take it as an input.
Not late interest
When less than the minimum is paid, the unpaid part carries late interest (gecikme faizi), a separate rate.
In Türkiye
Turkish banks quote the contractual rate monthly, before the KKDF and BSMV taxes: the rate in the installment formula is i = r × (1 + KKDF + BSMV). For credit cards the Central Bank of Türkiye (TCMB) sets a maximum. TCMB’s maximum monthly contractual rates since 1 January 2026: 3.25% for a statement balance under 30,000 TRY, 3.75% for 30,000–180,000 TRY and 4.25% above.