Simple Interest

Simple Interest Calculator — Formula I = P x r x t

The Simple Interest Calculator is a free online tool that computes interest, final amount, and period using the classic simple interest formula: I = P × r × t, where I is the interest earned, P is the principal (initial investment), r is the interest rate per period, and t is the number of periods. Enter any three of the four values and the calculator solves for the missing one, making it versatile for various financial and educational scenarios.Unlike compound interest where earnings are reinvested to generate interest on interest, simple interest is calculated only on the original principal — the interest earned each period is constant. This model applies to many real-world scenarios: short-term loans, promissory notes, treasury bills, car loans, and some bank deposits. The calculator shows a clear breakdown of principal versus interest and provides the formula used so you can verify the calculation. It handles daily, monthly, quarterly, and annual interest rate periods.Students studying financial mathematics use this to solve textbook problems and understand the difference between simple and compound interest. Business owners calculate interest on short-term commercial loans and supplier credit. Lenders compute interest earned on private loans. Accountants calculate interest for invoicing late payments (multa + juros). Legal professionals compute interest owed in contractual disputes where simple interest is specified. The calculator also helps compare the impact of simple vs. compound interest across different time horizons.Simple Interest Calculator is part of the facilita.tools financial toolkit. Available in Portuguese, English, and Spanish, optimized for desktop and mobile.