Simple Interest Calculator
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Simple interest is the most fundamental interest calculation in finance. Unlike compound interest—where accumulated interest earns additional interest over time—simple interest is calculated strictly on the original principal amount for the entire duration of the loan or deposit.
While most formal retail banking products in India (such as fixed deposits and mortgages) use compound interest, simple interest is widely used in short-term promissory notes, agricultural loans, informal peer-to-peer lending, and penalty interest calculations. The FinToolkit Simple Interest Calculator computes your exact interest and total maturity amount in seconds.
The statutory simple interest formula
Simple interest is calculated using the classic mathematical formula:
Total Amount (A) = P + SI
Where:
• P = Principal amount deposited or borrowed (₹)
• R = Annual interest rate percentage (% p.a.)
• T = Time period in years (or months converted to years: Months ÷ 12)
Worked calculation example
Consider an informal personal agreement or short-term loan of ₹1,00,000 lent at an interest rate of 8.00% per annum for a duration of 3 years.
| Calculation Component | Amount |
|---|---|
| Principal amount (P) | ₹1,00,000 |
| Annual interest rate (R) | 8.00% p.a. |
| Time period (T) | 3 years |
| Annual interest earned per year (₹1L × 8%) | ₹8,000 / year |
| Total simple interest earned (₹8,000 × 3) | ₹24,000 |
| Total repayment amount (Principal + Interest) | ₹1,24,000 |
Notice that the interest remains exactly ₹8,000 in Year 1, Year 2, and Year 3. The interest earned in previous years does not accumulate to generate fresh returns.
Simple Interest vs Compound Interest
- Constant vs exponential growth: In simple interest, growth is linear. In compound interest, growth accelerates exponentially because past interest is added to the principal for subsequent cycles.
- Compare the numbers: If that same ₹1,00,000 were compounded annually at 8% for 3 years, the total interest earned would be ₹25,971 (an extra ₹1,971). Over 10 years, compound interest earns ₹1,15,892 compared to just ₹80,000 in simple interest. Compare the difference using our Compound Interest Calculator.
Frequently asked questions
Where is simple interest used in India?
Simple interest is used in certain government crop loans, short-term treasury bills, non-banking promissory notes, informal lending between family members, and court-awarded delayed compensation.
How do I calculate simple interest for periods less than a year?
Convert the time into fractions of a year: for months, divide by 12 (e.g., 6 months = 6/12 = 0.5 years). For days, divide by 365 (e.g., 73 days = 73/365 = 0.2 years).
Is simple interest taxable in India?
Yes. Any interest earned on loans, promissory notes, or deposits is treated as "Income from Other Sources" and taxed at your regular slab rate.
Related financial calculators
- Compound Interest Calculator — compare linear simple interest against compounding growth.
- Fixed Deposit Calculator — see how bank deposits compound interest quarterly.
- Rule of 72 Calculator — estimate how quickly money doubles at a given interest rate.
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Every result is produced by a published formula running at full double precision in your browser. Only the displayed figures are rounded.
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Data sources
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