Simple Interest Calculator - Free Online

Principal Amount

₹

₹1,000₹1,00,00,000

Annual Interest Rate

136

Tenure

yrs

130

Total Amount

₹0

Total Interest

₹0

Interest Breakdown

Principal vs interest split

Principal

₹0

Total Interest

₹0

Total Amount

₹0

What is a Simple Interest?

A Simple Interest Calculator is a tool that computes the interest earned or owed on a principal amount using a fixed annual rate and a specified time period — without any compounding. Simple interest is the most straightforward form of interest calculation: the interest charge is applied exclusively to the original principal, making it linear and predictable across the entire tenure.

The concept is foundational to personal finance. Whether you are depositing money in a post office scheme, taking a short-term gold loan, or evaluating a flat-rate NBFC product, simple interest is the mechanism at work. In India, it is widely used in chit funds, cooperative bank deposits, and flat-rate vehicle loans — products that are especially prevalent in smaller cities and rural financial markets.

The formula is: SI = (P × R × T) ÷ 100, and the maturity amount is A = P + SI. There are no hidden assumptions, no compounding frequency variables, and no intermediate calculations. What you put in is what the formula operates on.

This stands in direct contrast to Compound Interest, where interest earned in one period is added to the principal before the next period's interest is calculated. Over a 10-year horizon, the difference between the two methods can be substantial. For a ₹1,00,000 investment at 10% p.a. over 10 years, simple interest yields ₹1,00,000 in interest (total amount ₹2,00,000), while compound interest (annually) yields ₹1,59,374 in interest (total ₹2,59,374) — a difference of nearly ₹60,000.

Understanding when a product uses simple versus compound interest is a critical financial literacy skill. This calculator helps you compute SI scenarios accurately in seconds, so you can make informed comparisons before committing to any deposit, loan, or lending arrangement.

How to use this Simple Interest calculator

Enter your Principal Amount — the original sum you are investing or borrowing in rupees. Use the slider for quick adjustments between ₹1,000 and ₹1,00,00,000, or type the exact amount directly. For most personal finance scenarios, values between ₹10,000 and ₹10,00,000 are typical.
Set the Annual Interest Rate — the fixed interest rate per annum as a percentage. If your lender or scheme quotes the rate in other periods (e.g. monthly or quarterly), convert it to annual first by multiplying: a 1% monthly rate equals 12% p.a. for simple interest purposes. Use the slider to explore rates between 1% and 36%.
Set the Tenure — the time period in complete years. For sub-year calculations, enter a decimal: 6 months = 0.5 years, 9 months = 0.75 years, 18 months = 1.5 years. The slider covers 1 to 30 years.
Read the Total Interest — this is the pure interest component. Compare this figure across different rate or tenure combinations to identify the cheapest or most rewarding option.
Check the Total Amount — the final figure you will receive or repay. Use this to confirm whether a scheme's promised maturity value is consistent with the stated rate, or to plan the cash outflow for a loan you are considering.
Explore what-if scenarios — move the sliders to see how adding one more year to a tenure or negotiating 1% off the rate changes your total interest. This real-time sensitivity analysis is where the calculator is most powerful.

Formula & Methodology

Simple Interest Formula:

SI = (P × R × T) ÷ 100

Total Amount:

A = P + SI

Variable definitions:
- P — Principal Amount (₹): the original sum of money invested or borrowed
- R — Annual Interest Rate (%): the fixed rate applied each year, unchanged throughout the tenure
- T — Time (years): the period for which the money is invested or borrowed
- SI — Simple Interest (₹): the interest earned or charged over the full tenure
- A — Total Amount (₹): the maturity value or total repayment amount

Worked example:

Principal: ₹75,000 | Rate: 9% p.a. | Tenure: 4 years

SI = (75,000 × 9 × 4) ÷ 100 = 27,00,000 ÷ 100 = ₹27,000

Total Amount = 75,000 + 27,000 = ₹1,02,000

The interest for each of the 4 years is identical at ₹6,750 (= ₹27,000 ÷ 4), which is the defining characteristic of simple interest — a flat, predictable charge year on year.

Key assumption: This calculator treats T as a whole or decimal number of years and applies R as an annual rate. No day-count conventions (actual/365, actual/360) are applied. For precise calculations on short-duration instruments where day-count matters — such as treasury bills or commercial paper — use the exact-day variant of the formula: SI = (P × R × D) ÷ (100 × 365), where D is the number of days.

Frequently Asked Questions

What is simple interest and how is it calculated?

Simple interest is a method of calculating interest where the charge is applied only to the original principal amount for every period of the loan or investment. It does not take into account previously earned or paid interest — making it linear and predictable. The formula is SI = (P × R × T) ÷ 100, where P is the principal, R is the annual rate, and T is the time in years. Unlike compound interest, the interest amount remains identical each year regardless of how long the money is held.

What is the difference between simple interest and compound interest?

Simple interest is calculated solely on the original principal, whereas compound interest is calculated on the principal plus all previously accumulated interest. This means compound interest grows exponentially over time, while simple interest grows linearly. For the same principal, rate, and tenure, compound interest always produces a higher maturity amount than simple interest. For a side-by-side comparison, use our [Compound Interest Calculator](/compound-interest-calculator/) alongside this tool.

What is the simple interest formula used in this calculator?

The calculator uses the standard formula: SI = (P × R × T) ÷ 100, where SI is the simple interest, P is the principal amount in rupees, R is the annual interest rate as a percentage, and T is the time period in years. The total maturity amount is then calculated as A = P + SI. No additional assumptions or adjustments are applied — the result is exactly what the formula produces.

Is simple interest used by banks in India?

Yes, simple interest is used by banks and non-banking financial companies (NBFCs) in India for certain products — most commonly for short-tenure loans, vehicle loans, and some personal loans where daily reducing balance is not applicable. However, savings accounts and fixed deposits in India typically use compound interest, which benefits depositors more. If you are comparing loan products, always confirm with your lender whether interest is calculated on a flat (simple) or reducing balance basis.

How do I calculate simple interest manually?

To calculate manually, multiply your principal (P) by the annual interest rate (R as a decimal or percentage) and the tenure in years (T), then divide by 100 if using the percentage form. For example: a principal of ₹50,000 at 10% p.a. for 3 years gives SI = (50,000 × 10 × 3) ÷ 100 = ₹15,000. Add this to the principal to get the total amount of ₹65,000. Our Simple Interest Calculator automates this instantly with sliders for quick what-if scenarios.

Which is better — simple interest or compound interest for investments?

For investments, compound interest is almost always better because your returns also earn returns over time, accelerating wealth creation significantly. Simple interest is predictable and transparent, which is useful for short-term deposits or understanding loan costs, but it underperforms compound interest for long-term wealth building. If you are planning a long-term investment, explore our [SIP Calculator](/sip-calculator/) to see how compounding works in the context of mutual fund investments.

Can I use this calculator for a loan to find total interest payable?

Yes, this calculator works for any simple interest scenario — including flat-rate loans. Enter the loan amount as the Principal Amount, the lender's stated annual interest rate, and the loan tenure in years to instantly see the total interest you will pay and the total repayment amount. Note that most home loans and personal loans in India use a reducing balance (EMI) method, not simple interest — for those, use our [Home Loan EMI Calculator](/home-loan-emi-calculator/) instead.

What is the minimum and maximum tenure I can calculate for?

This calculator supports tenures from 1 year to 30 years, covering most real-world use cases from short-term loans to long-horizon financial planning. For sub-year calculations (months or days), convert to a fractional year before entering — for example, 6 months = 0.5 years, 3 months = 0.25 years. The calculator accepts decimal values for the tenure field if you type them in directly.

Is the interest earned from simple interest investments taxable in India?

Yes, interest income in India is taxable under the head 'Income from Other Sources' as per the Income Tax Act. This applies whether the interest comes from a bank deposit, private lending, or any other arrangement using simple interest. The applicable tax rate depends on your income slab. If your total interest income from a single bank exceeds ₹40,000 in a financial year (₹50,000 for senior citizens), TDS may also be deducted — use our [TDS Calculator](/tds-calculator/) to estimate the deduction.

How does changing the interest rate affect my total interest?

In simple interest, the relationship between rate and total interest is perfectly linear — doubling the rate exactly doubles the interest, and halving the rate halves it. For example, at ₹1,00,000 principal over 5 years, a rate of 8% p.a. yields ₹40,000 in interest, while 16% p.a. yields ₹80,000. This linear property makes simple interest easy to reason about, unlike compound interest where rate changes have an exponential effect over long tenures.

Can this calculator be used for gold loans or vehicle loans in India?

Yes, several lenders in India — including gold loan NBFCs and some cooperative banks — charge interest on a flat or simple interest basis. For a gold loan, enter the sanctioned loan amount as the Principal Amount, the stated flat annual rate, and the loan tenure to instantly see your total interest outgo and repayment amount. Always verify with your lender whether the rate quoted is a flat rate or a reducing balance rate, as the two produce very different totals.

What is the difference between a flat interest rate and a reducing balance rate?

A flat interest rate (simple interest) applies the stated rate to the original principal for the entire tenure, so the interest component stays constant every month. A reducing balance rate applies the rate only to the outstanding principal, which decreases as you repay — resulting in lower overall interest. For the same nominal rate, the effective cost of a flat-rate loan is significantly higher than a reducing balance loan. Most EMI-based loans in India — home loans, car loans, personal loans — use the reducing balance method.