🧮 Simple Interest Calculator
Simple interest = principal × rate × time ÷ 100, interest accrues only on the original amount, never on interest. Enter your values below, results update instantly, entirely on your device.
50,000 × 7% × 3 years
How the simple interest calculator works
SI = P × R × T ÷ 100; total = principal + SI. Interest is charged only on the original principal each period. Because it is a fixed slice of the principal each year, the total grows in a straight line, doubling the time doubles the interest, unlike compounding, which accelerates.
Example: 50,000 at 7% for 3 years → interest 10,500; total 60,500.
Simple interest survives in short-term lending, some auto loans, bonds’ coupon math and school syllabi; most savings and mortgages compound instead. Same inputs at 7%/3 years compounded yearly would yield 11,252, the gap widens fast with time.
Frequently asked questions
What is the simple interest formula?
SI = P × R × T ÷ 100, with rate per year and time in years. 20,000 at 5% for 2 years = 2,000 interest.
What is the difference between simple and compound interest?
Simple interest is charged only on the principal every period; compound interest is charged on principal plus accumulated interest, so it grows faster over time.
How do I get the time in months?
Use fractional years: 9 months = 0.75 years. SI on 10,000 at 8% for 9 months = 10,000 × 8 × 0.75 ÷ 100 = 600.
When is simple interest actually used?
It's common for short-term and fixed arrangements: many car loans, some personal and student loans, and certain bonds and treasury instruments quote simple interest. Savings accounts and mortgages usually compound instead.
How do I find the rate or principal from simple interest?
Rearrange I = P × R × T ÷ 100. Rate = I × 100 ÷ (P × T); principal = I × 100 ÷ (R × T). For example, 600 interest on 10,000 over 0.75 years implies a rate of 600 × 100 ÷ (10,000 × 0.75) = 8%.
What is the total to repay on a simple-interest loan?
Add the interest to the principal: for 8,000 at 6% over 4 years, interest is 8,000 × 6 × 4 ÷ 100 = 1,920, so the total repayable is 9,920.
How do I handle a loan measured in days?
Convert days to a fraction of a year, usually days ÷ 365. For 10,000 at 9% over 90 days: 10,000 × 9 × (90 ÷ 365) ÷ 100 ≈ 221.9 interest.
Is this simple interest calculator accurate and private?
Yes. It uses the standard published formula, shows its working under every result, and computes locally in your browser, your inputs are never sent to a server, and the page works offline.