🧮 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.
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%.
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.