What Is Simple Interest?
Simple interest is the most basic method for calculating the cost of borrowing money or the return on a deposit. Unlike compound interest, simple interest is calculated only on the original principal amount — it never compounds on previously earned interest. This makes the interest amount the same in every period, growing linearly rather than exponentially over time.
Simple Interest Formula
SI = (P × R × T) ÷ 100
P
Principal — the original amount
R
Rate — annual interest rate (%)
T
Time — duration in years
Total Amount (Maturity Value) = P + SI = P(1 + RT/100)
For example: a $100,000 loan at 8% annual interest for 3 years generates SI = (100,000 × 8 × 3) ÷ 100 = $24,000 in interest, for a total repayment of $124,000.
Simple vs Compound Interest
The key difference between simple and compound interest is whether interest is calculated on just the principal, or on the principal plus all previously accumulated interest.
| Simple Interest | Compound Interest | |
|---|---|---|
| Calculated on | Original principal only | Principal + accumulated interest |
| Growth pattern | Linear (constant per period) | Exponential (grows each period) |
| Formula | SI = PRT / 100 | A = P(1 + R/100)ᵗ |
| Best for | Short-term loans, simple bonds | Long-term investments, savings |
| Favors | Borrowers (lower total cost) | Lenders/investors (higher returns) |
Real-World Simple Interest Examples
| Principal | Rate | Time | Interest | Total Amount |
|---|---|---|---|---|
| $50,000 | 6% | 1 yrs | $3,000 | $53,000 |
| $100,000 | 8% | 3 yrs | $24,000 | $124,000 |
| $250,000 | 10% | 2 yrs | $50,000 | $300,000 |
| $500,000 | 7.5% | 5 yrs | $187,500 | $687,500 |
| $1,000,000 | 9% | 4 yrs | $360,000 | $1,360,000 |
Where Simple Interest Is Used
Auto Loans
Many car loans use simple interest calculated on the outstanding principal.
Short-Term Loans
Personal loans and bridge loans under 1-2 years often use simple interest.
Treasury Bills
T-bills and certain government bonds calculate returns using simple interest.
Private Lending
Loans between friends, family, or informal lenders typically use simple interest for clarity.
Some Fixed Deposits
Certain short-term FDs and CDs pay simple interest rather than compounding.
Financial Education
Simple interest is the foundational concept taught before introducing compounding.
Frequently Asked Questions
Disclaimer: This calculator provides estimates based on the standard simple interest formula for educational and planning purposes. Actual loan or investment terms may include additional fees, different day-count conventions, or hybrid interest structures. Always consult your loan agreement or a financial advisor for exact figures.
Explore More Tools
Free EMI Calculator (Home, Car & Personal Loan)
Calculate EMI, monthly payments, total interest, and total repayment for home loans, car loans, personal loans, and mortgages. Free online loan calculator with instant results.
SIP Calculator
Calculate SIP returns, future investment value, wealth growth, and inflation-adjusted corpus. Supports Step-Up SIP and SIP + Lumpsum planning.
Compound Interest Calculator
Calculate compound interest, investment growth, future value, recurring contributions, and long-term savings projections with detailed yearly breakdowns.
Crypto Profit Calculator
Calculate cryptocurrency trading profits, losses, ROI, ROE, leverage exposure, fees, and liquidation risk for long and short positions.