Interest Rate Calculator
Calculate simple interest and total amount from principal, rate, and time.
How to use
Enter your values and pick a mode if the tool offers one.
Click calculate — results appear instantly, computed in your browser.
Copy the result or save the tool to your favorites.
Frequently asked questions
Simple interest: SI = P × R × T / 100.
Simple interest. For compounding, use the RD/FD maturity calculator.
Years. Convert months to a fraction of a year if needed.
It shows total interest over the full period; divide by months for a monthly figure.
In your browser only.
About the Interest Rate Calculator
This calculator computes simple interest on a sum of money and shows both the interest earned and the total amount after the term. It is the right tool when interest is charged or earned on the original principal only, without compounding.
How simple interest works
Simple interest uses the formula SI = P x R x T divided by 100, where P is the principal, R is the annual rate as a percentage, and T is the time in years. The interest is the same every year because it is always calculated on the original principal, never on accumulated interest. This makes simple interest straightforward to compute and predict, which is why it is common in short-term loans, certain fixed deposits, and many informal lending arrangements.
Simple versus compound interest
The key difference is what the interest is calculated on. Simple interest always uses the original principal, so the yearly interest is constant. Compound interest adds each period's interest to the balance, so future interest is calculated on a growing amount and the total accelerates over time. Over short periods the two are close, but over many years compound interest produces substantially more. If your situation involves compounding, such as most savings accounts and long-term deposits, use a compounding calculator instead for an accurate figure.
How to use it
Enter the principal, the annual interest rate, and the time in years. The calculator returns the total interest over the full period and the final amount including the principal. To find a monthly interest figure, divide the total by the number of months in the term.
Common uses
Simple interest calculations appear in short-term personal loans, vehicle loans quoted on a flat basis, certain bonds, and quick mental estimates of what a sum will earn or cost. It is also a useful baseline for understanding how much of a loan's cost comes purely from interest versus the principal you borrowed.
Tips and caveats
Make sure your rate and time use the same unit; this tool expects an annual rate and time in years, so convert months to a fraction of a year if needed. Be aware that flat or simple interest quoted on a loan can look cheaper than an equivalent reducing-balance or compound rate, so compare carefully. For loans repaid in monthly installments on a reducing balance, the EMI Calculator is more appropriate, and for compounding deposits use the RD/FD Maturity Calculator. All figures are calculated in your browser.