Simple Interest Calculator
Calculate simple (non-compounding) interest and total balance.
Simple interest is charged only on the original principal — common for short-term loans.
How the Math Works
The simple interest calculator uses the formula interest = P × r × t, where P is the principal amount (initial sum), r is the annual interest rate expressed as a decimal, and t is the time in years. This calculation determines only the interest earned or paid without compounding - meaning interest is calculated solely on the original principal throughout the entire period. For example, if you invest $1,000 at 5% annual simple interest for 3 years, the interest earned would be $150 (1000 × 0.05 × 3).
Practical Applications
To use this calculator practically, first convert your interest rate from percentage to decimal form (5% becomes 0.05), then multiply the principal amount by this rate and then by the number of years the money is invested or borrowed. This tool is particularly useful for comparing short-term loans, certificates of deposit, or understanding the cost of borrowing money over brief periods. Simply enter your principal, rate, and time to instantly see both the interest accrued and your total balance.
Day-to-Day Use
Simple interest calculations help you make informed financial decisions in everyday situations like choosing between different savings accounts, evaluating personal loan offers, or understanding the true cost of short-term financing options. When shopping for a car loan or considering a certificate of deposit, this calculator quickly reveals how much interest you'll earn or pay, helping you compare options and select the most favorable terms for your specific situation without needing to negotiate or research complex financial products.
Worked example
$1,000 at 5% for 3 years → 1000 × 0.05 × 3 = $150 interest.
FAQ
Simple vs compound?
Simple interest grows linearly; compound interest grows exponentially and ends up larger over time.