Loan Interest Calculator 2026

Simple interest method: interest = principal × (annual_rate / 100 / 12) × number_of_months. Example: PLN 100,000 at 8% for 12 months = PLN 8,000 in interest.

The nominal rate is the stated annual rate. The effective annual rate (EAR) accounts for monthly compounding: EAR = (1 + r/12)^12 − 1. The calculator uses the nominal rate.

The loan interest rate covers only the cost of the principal. APR (Annual Percentage Rate, RRSO in Polish) also includes fees and insurance — it is always higher and gives a fuller picture of the true borrowing cost.

Interest increases linearly with the rate. Raising the rate from 8% to 9% on PLN 100,000 for 12 months adds PLN 1,000 in interest (from PLN 8,000 to PLN 9,000).

The simple method is used for short-term loans, some working-capital credit lines and quick estimates. For instalment loans banks use the annuity (declining-balance) formula.

For businesses (sole traders, companies), interest on loans taken for business purposes is a deductible expense. Interest on consumer loans is not deductible. Consult a tax adviser for specifics.

Simple method: 200,000 × 7% / 12 × 24 = PLN 28,000. Under the annuity method total interest would be somewhat lower because the outstanding balance decreases with each payment.

Shorten the repayment term, negotiate a lower rate, make a larger down payment or make overpayments — each reduces the principal and therefore the interest base.

The simple method calculates interest on the full principal for the entire term — the result is overstated. The annuity method calculates interest on the declining balance — each payment reduces the base. The difference grows with longer terms.

No — results are indicative, based on the simple interest method. Actual loan cost (APR, fees, repayment schedule) is specified in the loan agreement with the lender.