What Is Simple Interest?
Simple interest is a method of calculating the interest charge or return on a principal sum over a specified period. Unlike compound interest, simple interest does not add accumulated interest back into the principal pool; hence, the interest earned or charged remains constant in every single period.
Simple Interest Formula
$$I = P \times r \times t$$
$$\text{Total Maturity Amount} (A) = P + I$$
- P = Principal amount (initial investment or loan)
- r = Annual interest rate (expressed as a decimal or percentage divided by 100)
- t = Time duration of the loan or investment in years
Simple Interest Calculation Example
If you invest ₹100,000 at an annual simple interest rate of 8% for 3 years:
- Interest ($I$) = $100,000 \times 0.08 \times 3 = \text{₹}24,000$
- Total Maturity Amount ($A$) = $100,000 + 24,000 = \text{₹}124,000$
Simple Interest vs. Compound Interest
| Feature | Simple Interest | Compound Interest |
|---|---|---|
| Interest Basis | Calculated strictly on original principal | Calculated on principal plus accumulated past interest |
| Growth Pattern | Linear growth over time | Exponential growth over time |
| Common Applications | Short-term loans, auto loans, specific bonds | Savings accounts, mortgages, long-term investments |
Frequently Asked Questions (FAQ)
What is a simple interest calculator?
A financial tool that computes interest accrued or owed over time based on an unchanging principal amount.
How do I calculate simple interest manually?
Multiply the principal amount by the annual interest rate (in decimal format) and by the time duration in years ($P \times r \times t$).
How is time converted if duration is in months or days?
For months, divide the total months by 12. For days, divide the total days by 365 to convert into standard fractional years.
Is simple interest used for credit cards?
No, credit cards typically use daily compound interest. Simple interest is more common in short-term personal or vehicle loans.