Simple Interest Calculator
Calculate simple interest from principal, rate, and time.
Simple interest is calculated only on the original principal, making it straightforward to understand and predict. It appears in short-term loans, certificates of deposit, and late-payment penalties. Enter your principal, rate, and time period below to see the exact interest amount and total repayment.
Your result will appear here...
How to Calculate Simple Interest
- Enter the principal amount — the initial sum of money.
- Enter the annual interest rate — as a percentage.
- Enter the time period — in years (use decimals for months, e.g., 0.5 for 6 months).
- Click Calculate — the tool shows the interest earned and the total amount (principal + interest).
Frequently Asked Questions
What is simple interest? ▼
Simple interest is calculated only on the original principal amount: Interest = Principal × Rate × Time (I = P × R × T). Unlike compound interest, it does not add earned interest back to the principal. A $1,000 loan at 5% for 3 years accrues $150 in simple interest ($1,000 × 0.05 × 3).
Where is simple interest used? ▼
Simple interest is used in: short-term personal loans, car loans, some bonds, promissory notes, late payment penalties, and certificates of deposit (CDs) with fixed terms. Most mortgages and savings accounts use compound interest instead.
What is the difference between simple and compound interest? ▼
Simple interest is calculated only on the principal. Compound interest is calculated on the principal plus previously earned interest. Over time, compound interest grows much faster. On $10,000 at 8% for 20 years: simple interest yields $26,000 total, compound interest yields $46,610.
How do I calculate monthly simple interest? ▼
For monthly calculations, convert the annual rate to a monthly rate (divide by 12) and use months instead of years. Alternatively, express months as a decimal of years: 6 months = 0.5 years. $5,000 at 6% for 6 months: $5,000 × 0.06 × 0.5 = $150.
Can I use this for late payment interest? ▼
Yes. Many invoices specify late fees as simple interest (e.g., 1.5% per month). Enter the overdue amount as principal, the monthly rate as an annual equivalent, and the overdue period as time.
Is my data stored? ▼
No. All calculations run in your browser. No data is sent to any server.
Why Use This Tool?
What does Simple Interest Calculator do? ▼
Calculate simple interest from principal, rate, and time.
Is my data uploaded? ▼
No. ToolMasta tools run in your browser and do not require signup or server-side processing for normal usage.
Can I use it for free? ▼
Yes. This tool is free to use with no sign-up required.