Calculate Simple & Compound Interest
How the Interest Calculator Works
Interest is the cost of using money - whether you're borrowing it or lending it. Our Interest Calculator lets you compute both Simple Interest and Compound Interest instantly. Enter your principal amount, annual interest rate, and investment period, and the calculator returns the exact interest earned and total maturity value. Switch between Simple and Compound modes to see how the same inputs produce dramatically different outcomes over time.
For compound interest, you can also select the compounding frequency - annually, semi-annually, quarterly, monthly, or daily. The more frequently interest compounds, the higher your effective return or cost.
Simple Interest vs. Compound Interest — Key Formulas
Simple Interest
SI = (P × R × T) / 100 | A = P + SI
Where P is the principal, R is the annual rate in percent, and T is time in years. Interest is computed only on the original principal — it does not compound. The period unit you select (days / months / years) is converted to years before applying the formula: days ÷ 365 or months ÷ 12.
| Variable | Meaning | Example Value |
|---|---|---|
| SI | Simple Interest earned | ₹32,500 |
| P | Principal — initial amount deposited or borrowed | ₹1,00,000 |
| R | Annual interest rate (%) | 6.5 |
| T | Time in years (days ÷ 365 or months ÷ 12) | 5 |
| A | Total value = P + SI | ₹1,32,500 |
Worked Example — ₹1,00,000 at 6.5% for 5 Years (Simple Interest)
P = ₹1,00,000
R = 6.5% | T = 5 years
SI = (1,00,000 × 6.5 × 5) / 100 = ₹32,500
Total Value = ₹1,00,000 + ₹32,500 = ₹1,32,500
Compound Interest
A = P × (1 + (R / 100) / n) ^ (n × T) | CI = A − P
Where n is the compounding frequency per year (1 = Annually, 2 = Semi-Annually, 4 = Quarterly, 12 = Monthly, 365 = Daily). Each period, interest is added to the principal and the next period's interest is calculated on the new balance — causing exponential growth. The same period-unit conversion (days ÷ 365, months ÷ 12) is applied to T before calculating.
| Variable | Meaning | Example Value |
|---|---|---|
| A | Total maturity amount | ₹1,38,290 |
| P | Principal — initial amount deposited or borrowed | ₹1,00,000 |
| R | Annual interest rate (%) | 6.5 |
| n | Compounding frequency per year | 12 (Monthly) |
| T | Time in years (days ÷ 365 or months ÷ 12) | 5 |
| CI | Compound Interest = A − P | ₹38,290 |
Worked Example — ₹1,00,000 at 6.5% for 5 Years (Monthly Compounding)
P = ₹1,00,000 | R = 6.5% | n = 12 | T = 5
(R / 100) / n = (6.5 / 100) / 12 = 0.005417 per month
n × T = 12 × 5 = 60 periods
A = 1,00,000 × (1.005417)^60 ≈ ₹1,38,284
CI = ₹1,38,284 − ₹1,00,000 = ₹38,284
Who Uses an Interest Calculator - and Why
Whether you're a borrower, investor, or financial planner, understanding interest is fundamental. Here are the most common real-world scenarios where this calculator is essential:
🏦 Fixed Deposits
Banks quote an annual rate, but FDs compound quarterly or monthly. Use this calculator to see your actual maturity amount - not just the headline rate.
💳 Credit Card Debt
Credit cards compound daily at rates of 2–4% per month. Calculate how a ₹50,000 balance snowballs if you only pay the minimum - and motivate faster repayment.
📈 SIP & Investments
Estimate the compound growth potential of mutual fund or recurring deposit investments before committing to a savings goal.
🚗 Auto & Personal Loans
Many lenders advertise "flat" simple interest rates. Use this tool to compare flat vs. reducing-balance interest and make an informed borrowin decision.
🎓 Education Loans
Education loans often have a moratorium period where interest accrues without repayment. Model the total cost before the repayment phase begins.
👴 Retirement Planning
See the power of early investing. A 25-year-old investing ₹5 lakhs at 10% compounded annually will have over ₹87 lakhs by 65 - with zero additional contributions.
For a structured investment that earns compound interest on a fixed lump sum, use our FD Calculator to model maturity amounts across different compounding frequencies and tenures. If you're calculating the interest cost of a home, car, or personal loan, our Loan EMI Calculator provides a full amortization schedule showing principal and interest breakdown month by month.
Understanding Your Interest Results
Here's what each figure in your result panel means:
Total Interest - The net amount earned or owed beyond your original principal. This is the headline figure most borrowers and investors care about.
Principal Amount - Your original deposit or loan amount, shown for reference alongside the interest figure.
Total Value - Principal + Total Interest. This is the maturity value of your investment, or the total amount you will repay on a loan.
Donut Chart - A visual breakdown of how much of your total value is principal vs. interest, making the true cost or gain instantly clear.
Frequently Asked Questions
What is the difference between Simple and Compound Interest?
Which compounding frequency gives the highest return?
When should I use Simple Interest vs. Compound Interest mode?
How does the investment period unit (days/months/years) affect the result?
Is the interest calculator suitable for loan repayment planning?
Is my financial data stored or shared?
Financial Disclaimer
Mutual fund investments are subject to market risks. Please read all scheme related documents carefully before investing. Past performance of the schemes is neither an indicator nor a guarantee of future performance.
The purpose of this calculator is to inform the user and provide estimates. Do not plan your finances based solely on the calculator results.